input_description -distribution {Quantum Espresso} -package PWscf -program pw.x {

    toc {}

    intro {
        @b {Input data format:} { } = optional, [ ] = it depends, | = or
        
        All quantities whose dimensions are not explicitly specified are in
        RYDBERG ATOMIC UNITS. Charge is "number" charge (i.e. not multiplied 
        by e); potentials are in energy units (i.e. they are multiplied by e).
        
        @b BEWARE: TABS, DOS <CR><LF> CHARACTERS ARE POTENTIAL SOURCES OF TROUBLE 

        Comment lines in @i namelists can be introduced by a "!", exactly as in 
        fortran code. Comments lines in @i cards can be introduced by 
        either a "!" or a "#" character in the first position of a line.
        Do not start any line in @i cards with a "/" character.

        
        @b {Structure of the input data:}
        ===============================================================================
        
        @b &CONTROL
          ...
        @b /

        @b &SYSTEM
          ...
        @b /

        @b &ELECTRONS
          ...
        @b /

        [ @b &IONS
          ...
         @b / ]

        [ @b &CELL
          ...
         @b / ]

        @b ATOMIC_SPECIES
         X  Mass_X  PseudoPot_X
         Y  Mass_Y  PseudoPot_Y
         Z  Mass_Z  PseudoPot_Z

        @b ATOMIC_POSITIONS { alat | bohr | crystal | angstrom | crystal_sg }
          X 0.0  0.0  0.0  {if_pos(1) if_pos(2) if_pos(3)}
          Y 0.5  0.0  0.0
          Z O.0  0.2  0.2

        @b K_POINTS { tpiba | automatic | crystal | gamma | tpiba_b | crystal_b | tpiba_c | crystal_c }
        if (gamma)
           nothing to read
        if (automatic)
           nk1, nk2, nk3, k1, k2, k3
        if (not automatic)
           nks
           xk_x, xk_y, xk_z,  wk

        [ @b CELL_PARAMETERS { alat | bohr | angstrom }
           v1(1) v1(2) v1(3)
           v2(1) v2(2) v2(3)
           v3(1) v3(2) v3(3) ]

        [ @b OCCUPATIONS
           f_inp1(1)  f_inp1(2)  f_inp1(3) ... f_inp1(10)
           f_inp1(11) f_inp1(12) ... f_inp1(nbnd)
         [ f_inp2(1)  f_inp2(2)  f_inp2(3) ... f_inp2(10)
           f_inp2(11) f_inp2(12) ... f_inp2(nbnd) ] ]

        [ @b CONSTRAINTS
           nconstr  { constr_tol }
           constr_type(.)   constr(1,.)   constr(2,.) [ constr(3,.)   constr(4,.) ] { constr_target(.) } ]

        [ @b ATOMIC_FORCES
           label_1 Fx(1) Fy(1) Fz(1)
           .....
           label_n Fx(n) Fy(n) Fz(n) ]
    }

    #
    # namelist CONTROL
    #

    namelist CONTROL {

        var calculation -type CHARACTER {
            default { 'scf' }
            options {
                info {
                    A string describing the task to be performed. Options are:
                }
                opt -val 'scf' {} 
                opt -val 'nscf' {} 
                opt -val 'bands' {} 
                opt -val 'relax' {} 
                opt -val 'md' {}
                opt -val 'vc-relax' {} 
                opt -val 'vc-md' {}

                info {
                    (vc = variable-cell).
                }
            }
        }
        
        var title -type CHARACTER {
            default {' '}
            info {
                reprinted on output.
            }
        }
        
        var verbosity -type CHARACTER {
            default { 'low' }
            options {
                info {
                    Currently two verbosity levels are implemented:
                }
                opt -val 'high' {}
                opt -val 'low' {}

                info {
                    @b 'debug' and @b 'medium' have the same effect as @b 'high';
                    @b 'default' and @b 'minimal' as @b 'low'
                }
            }
        }
        
        var restart_mode -type CHARACTER {
            default { 'from_scratch' }
            options {
                info { Available options are: }

                opt -val 'from_scratch' {
                    From scratch. This is the normal way to perform a PWscf calculation
                }
                
                opt -val 'restart' {
                    From previous interrupted run. Use this switch only if you want to
                    continue an interrupted calculation, not to start a new one, or to
                    perform non-scf calculations.  Works only if the calculation was
                    cleanly stopped using variable @ref max_seconds, or by user request
                    with an "exit file" (i.e.: create a file "prefix".EXIT, in directory
                    "outdir"; see variables @ref prefix, @ref outdir).  Overrides @ref startingwfc
                    and @ref startingpot.
                }
            }   
        }
        
        var wf_collect -type LOGICAL { 
            default { .FALSE. }
            info {
                This flag controls the way wavefunctions are stored to disk :

                .TRUE.  collect wavefunctions from all processors, store them
                        into the output data directory "outdir"/"prefix".save,
                        ...

                        .FALSE. do not collect wavefunctions, leave them in temporary
                                local files (one per processor). The resulting format
                                ...

                Note that this flag has no effect on reading, only on writing.
            }
        }
        

        var nstep -type INTEGER {
            info {
                number of molecular-dynamics or structural optimization steps 
                performed in this run
            }
            default {
                1  if @ref calculation == 'scf', 'nscf', 'bands';
                50 for the other cases
            }
        }
        
        var iprint -type INTEGER {
            default { write only at convergence }
            info {
                band energies are written every @i iprint iterations
            }
        }
        
        var tstress -type LOGICAL {
            default { .false. }
            info {
                calculate stress. It is set to .TRUE. automatically if
                @ref calculation == 'vc-md' or 'vc-relax'
            }
        }
        
        
        var tprnfor -type LOGICAL {
            info {
                calculate forces. It is set to .TRUE. automatically if
                @ref calculation == 'relax','md','vc-md'
            }
        }
        
        var dt -type REAL { 
            default { 20.D0 }
            info {
                time step for molecular dynamics, in Rydberg atomic units
                (1 a.u.=4.8378 * 10^-17 s : beware, the CP code uses
                 Hartree atomic units, half that much!!!)
            }
        }
        
        var outdir -type CHARACTER { 
            default { 
                value of the ESPRESSO_TMPDIR environment variable if set; 
                current directory ('./') otherwise 
            }
            info {
                input, temporary, output files are found in this directory,
                see also @ref wfcdir
            }
        }

        var wfcdir -type CHARACTER { 
            default { same as @ref outdir }
            info {
                This directory specifies where to store files generated by
                each processor (*.wfc{N}, *.igk{N}, etc.). Useful for
                machines without a parallel file system: set @ref wfcdir to
                a local file system, while @ref outdir should be a parallel
                or networkfile system, visible to all processors. Beware:
                in order to restart from interrupted runs, or to perform
                further calculations using the produced data files, you
                may need to copy files to @ref outdir. Works only for pw.x.
            }
        }
        
        var prefix -type CHARACTER { 
            default { 'pwscf' }
            info {
                prepended to input/output filenames:
                prefix.wfc, prefix.rho, etc.
            }
        }

        var lkpoint_dir -type LOGICAL { 
            default { .true. }
            info {
                If .false. a subdirectory for each k_point is not opened
                in the "prefix".save directory; Kohn-Sham eigenvalues are
                stored instead in a single file for all k-points. Currently
                doesn't work together with @ref wf_collect
            }
        }
                
        var max_seconds -type REAL { 
            default { 1.D+7, or 150 days, i.e. no time limit }
            info {
                Jobs stops after @ref max_seconds CPU time. Use this option 
                in conjunction with option @ref restart_mode if you need to
                split a job too long to complete into shorter jobs that
                fit into your batch queues.
            }       
        }

        var etot_conv_thr -type REAL { 
            default { 1.0D-4 }
            info {
                Convergence threshold on total energy (a.u) for ionic
                minimization: the convergence criterion is satisfied
                when the total energy changes less than @ref etot_conv_thr
                between two consecutive scf steps. Note that @ref etot_conv_thr
                is extensive, like the total energy.
                See also @ref forc_conv_thr - both criteria must be satisfied
            }
        }

        var forc_conv_thr -type REAL { 
            default { 1.0D-3 }
            info {
                Convergence threshold on forces (a.u) for ionic minimization:
                the convergence criterion is satisfied when all components of 
                all forces are smaller than @ref forc_conv_thr.
                See also @ref etot_conv_thr - both criteria must be satisfied
            }
        }
                
        var disk_io -type CHARACTER { 
            default { see below }
            options {
                info {
                    Specifies the amount of disk I/O activity:
                }

                opt -val 'high' {
                    save all data to disk at each SCF step
                }

                opt -val 'medium' {
                    save wavefunctions at each SCF step unless
                    there is a single k-point per process (in which
                    case the behavior is the same as 'low')
                }

                opt -val 'low' {
                    store wfc in memory, save only at the end
                }

                opt -val 'none' {
                    do not save anything, not even at the end
                    ('scf', 'nscf', 'bands' calculations; some data
                    may be written anyway for other calculations)
                }
            
                info {
                    @b Default is @b 'low' for the scf case, @b 'medium' otherwise.
                    Note that the needed RAM increases as disk I/O decreases!
                    It is no longer needed to specify 'high' in order to be able
                    to restart from an interrupted calculation (see @ref restart_mode)
                    but you cannot restart in @ref disk_io=='none'
                }
            }
        }

        var pseudo_dir -type CHARACTER { 
            default { 
                value of the $ESPRESSO_PSEUDO environment variable if set; 
                '$HOME/espresso/pseudo/' otherwise 
            }
            info {
                directory containing pseudopotential files
            }
        }

        var tefield -type LOGICAL { 
            default { .FALSE. }
            info {
                If .TRUE. a saw-like potential simulating an electric field
                is added to the bare ionic potential. See variables @ref edir,
                @ref eamp, @ref emaxpos, @ref eopreg for the form and size of
                the added potential.

            }
        }

        var dipfield -type LOGICAL { 
            default { .FALSE. }
            info {
                If .TRUE. and @ref tefield==.TRUE. a dipole correction is also
                added to the bare ionic potential - implements the recipe
                of L. Bengtsson, PRB 59, 12301 (1999). See variables @ref edir,
                @ref emaxpos, @ref eopreg for the form of the correction. Must
                be used ONLY in a slab geometry, for surface calculations,
                with the discontinuity FALLING IN THE EMPTY SPACE.
            }
        }

        var lelfield -type LOGICAL { 
            default { .FALSE. }
            info {
                If .TRUE. a homogeneous finite electric field described
                through the modern theory of the polarization is applied.
                This is different from @ref tefield == .true. !
            }
        }
        
        var nberrycyc -type INTEGER { 
            default { 1 }
            info {
                In the case of a finite electric field  ( @ref lelfield == .TRUE. )
                it defines the number of iterations for converging the
                wavefunctions in the electric field Hamiltonian, for each
                external iteration on the charge density
            }
        }

       var lorbm -type LOGICAL { 
            default { .FALSE. }
            info {
                If @b .TRUE. perform orbital magnetization calculation.
                If finite electric field is applied (@ref lelfield==.true.) only Kubo terms are computed 
                [for details see New J. Phys. 12, 053032 (2010), doi:10.1088/1367-2630/12/5/053032].

		The type of calculation is @b 'nscf' and should be performed on an automatically
		generated uniform grid of k points.

		Works ONLY with norm-conserving pseudopotentials.
            }
        }

        var lberry -type LOGICAL {  
            default { .FALSE. }
            info {
                If .TRUE. perform a Berry phase calculation.
                See the header of PW/src/bp_c_phase.f90 for documentation.
            }
        }
                
        var gdir -type INTEGER {
            info {
               For Berry phase calculation: direction of the k-point
               strings in reciprocal space. Allowed values: 1, 2, 3
               1=first, 2=second, 3=third reciprocal lattice vector
               For calculations with finite electric fields
               (@ref lelfield==.true.) "gdir" is the direction of the field.
            }
        }

        var nppstr -type INTEGER {
            info {
                For Berry phase calculation: number of k-points to be
                calculated along each symmetry-reduced string.
                The same for calculation with finite electric fields
                (@ref lelfield==.true.).
            }
        }
        
        var lfcpopt -type LOGICAL {
            see { fcp_mu }
            default { .FALSE. }
            info {
                If .TRUE. perform a constant bias potential (constant-mu) calculation
                for a static system with ESM method. See the header of PW/src/fcp.f90 
                for documentation.

                NB:
                - The total energy displayed in 'prefix.out' includes the potentiostat
                  contribution (-mu*N).
                - @ref calculation must be 'relax'. 
                - @ref assume_isolated = 'esm' and @ref esm_bc = 'bc2' or 'bc3' must be set
                  in @ref SYSTEM namelist.
            }
        }

        var monopole -type LOGICAL {
            default { .FALSE. }
            see { zmon, realxz, block, block_1, block_2, block_height }
            info {
                In the case of charged cells (@ref tot_charge .ne. 0) setting monopole = .TRUE.
                represents the counter charge (i.e. -tot_charge) not by a homogenous
                background charge but with a charged plate, which is placed at @ref zmon
                (see below). Details of the monopole potential can be found in
                T. Brumme, M. Calandra, F. Mauri; PRB 89, 245406 (2014).
                Note, that in systems which are not symmetric with respect to the plate,
                one needs to enable the dipole correction! (@ref dipfield=.true.).
                Currently, symmetry can be used with monopole=.true. but carefully check
                that no symmetry is included which maps @i z to -@i z even if in principle one
                could still use them for symmetric systems (i.e. no dipole correction).
                For @ref nosym=.false. verbosity is set to 'high'.
            }
        }

    }
    

    #
    # NAMELIST &SYSTEM
    #

    namelist SYSTEM {

        var ibrav -type INTEGER {
            status { REQUIRED }
            info {
                Bravais-lattice index. If ibrav /= 0, specify EITHER
                [ @ref celldm(1)-@ref celldm(6) ] OR [ @ref A, @ref B, @ref C, @ref cosAB, @ref cosAC, @ref cosBC ]
                but NOT both. The lattice parameter "alat" is set to
                alat = celldm(1) (in a.u.) or alat = A (in Angstrom);
                see below for the other parameters.
                For ibrav=0 specify the lattice vectors in @ref CELL_PARAMETERS,
                optionally the lattice parameter alat = celldm(1) (in a.u.) 
                or = A (in Angstrom), or else it is taken from @ref CELL_PARAMETERS 
 
              ibrav      structure                   celldm(2)-celldm(6)
                                                   or: b,c,cosab,cosac,cosbc 
                0          free 
                    crystal axis provided in input: see card @ref CELL_PARAMETERS

                1          cubic P (sc) 
                    v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,1)

                2          cubic F (fcc)
                    v1 = (a/2)(-1,0,1),  v2 = (a/2)(0,1,1), v3 = (a/2)(-1,1,0)

                3          cubic I (bcc)
                    v1 = (a/2)(1,1,1),  v2 = (a/2)(-1,1,1),  v3 = (a/2)(-1,-1,1)

                4          Hexagonal and Trigonal P        celldm(3)=c/a
                    v1 = a(1,0,0),  v2 = a(-1/2,sqrt(3)/2,0),  v3 = a(0,0,c/a)

                5          Trigonal R, 3fold axis c        celldm(4)=cos(alpha)
                    The crystallographic vectors form a three-fold star around 
                    the z-axis, the primitive cell is a simple rhombohedron:
                    v1 = a(tx,-ty,tz),   v2 = a(0,2ty,tz),   v3 = a(-tx,-ty,tz)
                    where c=cos(alpha) is the cosine of the angle alpha between
                    any pair of crystallographic vectors, tx, ty, tz are:
                      tx=sqrt((1-c)/2), ty=sqrt((1-c)/6), tz=sqrt((1+2c)/3)
               -5          Trigonal R, 3fold axis <111>    celldm(4)=cos(alpha)
                    The crystallographic vectors form a three-fold star around 
                    <111>. Defining a' = a/sqrt(3) :
                    v1 = a' (u,v,v),   v2 = a' (v,u,v),   v3 = a' (v,v,u)
                    where u and v are defined as
                      u = tz - 2*sqrt(2)*ty,  v = tz + sqrt(2)*ty
                    and tx, ty, tz as for case ibrav=5
                    Note: if you prefer x,y,z as axis in the cubic limit,
                          set  u = tz + 2*sqrt(2)*ty,  v = tz - sqrt(2)*ty
                          See also the note in Modules/latgen.f90 
              
                6          Tetragonal P (st)               celldm(3)=c/a
                    v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,c/a)

                7          Tetragonal I (bct)              celldm(3)=c/a
                    v1=(a/2)(1,-1,c/a),  v2=(a/2)(1,1,c/a),  v3=(a/2)(-1,-1,c/a)

                8          Orthorhombic P                  celldm(2)=b/a
                                                           celldm(3)=c/a
                    v1 = (a,0,0),  v2 = (0,b,0), v3 = (0,0,c)

                9          Orthorhombic base-centered(bco) celldm(2)=b/a
                                                           celldm(3)=c/a
                    v1 = (a/2, b/2,0),  v2 = (-a/2,b/2,0),  v3 = (0,0,c)
               -9          as 9, alternate description
                    v1 = (a/2,-b/2,0),  v2 = (a/2, b/2,0),  v3 = (0,0,c)

               10          Orthorhombic face-centered      celldm(2)=b/a
                                                           celldm(3)=c/a
                    v1 = (a/2,0,c/2),  v2 = (a/2,b/2,0),  v3 = (0,b/2,c/2)

               11          Orthorhombic body-centered      celldm(2)=b/a
                                                           celldm(3)=c/a
                    v1=(a/2,b/2,c/2),  v2=(-a/2,b/2,c/2),  v3=(-a/2,-b/2,c/2)

               12          Monoclinic P, unique axis c     celldm(2)=b/a
                                                           celldm(3)=c/a,
                                                           celldm(4)=cos(ab)
                    v1=(a,0,0), v2=(b*cos(gamma),b*sin(gamma),0),  v3 = (0,0,c)
                    where gamma is the angle between axis a and b. 
              -12          Monoclinic P, unique axis b     celldm(2)=b/a
                                                           celldm(3)=c/a,
                                                           celldm(5)=cos(ac)
                    v1 = (a,0,0), v2 = (0,b,0), v3 = (c*cos(beta),0,c*sin(beta))
                    where beta is the angle between axis a and c

               13          Monoclinic base-centered        celldm(2)=b/a
                                                           celldm(3)=c/a,
                                                           celldm(4)=cos(ab)
                    v1 = (  a/2,         0,                -c/2),
                    v2 = (b*cos(gamma), b*sin(gamma), 0),
                    v3 = (  a/2,         0,                  c/2),
                    where gamma is the angle between axis a and b

               14          Triclinic                       celldm(2)= b/a,
                                                           celldm(3)= c/a,
                                                           celldm(4)= cos(bc),
                                                           celldm(5)= cos(ac),
                                                           celldm(6)= cos(ab)
                    v1 = (a, 0, 0),
                    v2 = (b*cos(gamma), b*sin(gamma), 0)
                    v3 = (c*cos(beta),  c*(cos(alpha)-cos(beta)cos(gamma))/sin(gamma),
                         c*sqrt( 1 + 2*cos(alpha)cos(beta)cos(gamma)
                                   - cos(alpha)^2-cos(beta)^2-cos(gamma)^2 )/sin(gamma) )
                    where alpha is the angle between axis b and c
                           beta is the angle between axis a and c
                          gamma is the angle between axis a and b
            }   
        }
        
        group {
            label { Either: }

            dimension celldm -start 1 -end 6 -type REAL {
                see  { ibrav }
                info {
                    Crystallographic constants - see the @ref ibrav variable.
                    Specify either these OR @ref A,@ref B,@ref C,@ref cosAB,@ref cosBC,@ref cosAC NOT both.
                    Only needed values (depending on "ibrav") must be specified
                    alat = @ref celldm(1) is the lattice parameter "a" (in BOHR)
                    If @ref ibrav==0, only @ref celldm(1) is used if present; 
                    cell vectors are read from card @ref CELL_PARAMETERS
                }
            }

            label { Or: }

            vargroup -type REAL {
                var A
                var B
                var C
                var cosAB
                var cosAC
                var cosBC
                see { ibrav }
                info {
                    Traditional crystallographic constants:
                    
                      a,b,c in ANGSTROM               
                      cosAB = cosine of the angle between axis a and b (gamma)
                      cosAC = cosine of the angle between axis a and c (beta)
                      cosBC = cosine of the angle between axis b and c (alpha)

                    The axis are chosen according to the value of @ref ibrav.
                    Specify either these OR @ref celldm but NOT both.
                    Only needed values (depending on @ref ibrav) must be specified.

                    The lattice parameter alat = A (in ANGSTROM ).

                    If @ref ibrav == 0, only A is used if present, and 
                    cell vectors are read from card @ref CELL_PARAMETERS.
                }
            }
        }
                                                   
        var nat -type INTEGER {
            status { REQUIRED }
            info {
                number of atoms in the unit cell (ALL atoms, except if 
                space_group is set, in which case, INEQUIVALENT atoms)
            }
        }
        
        var ntyp -type INTEGER {
            status { REQUIRED }     
            info {
                number of types of atoms in the unit cell
            }
        }

        var nbnd -type INTEGER {
            default {
                for an insulator, @ref nbnd = number of valence bands
                (@ref nbnd = # of electrons /2);
                @br for a metal, 20% more (minimum 4 more)
            }
            info {
                Number of electronic states (bands) to be calculated.
                Note that in spin-polarized calculations the number of
                k-point, not the number of bands per k-point, is doubled
            }
        }
        
        var tot_charge -type REAL { 
            default { 0.0 }
            info {
                Total charge of the system. Useful for simulations with charged cells.
                By default the unit cell is assumed to be neutral (tot_charge=0). 
                tot_charge=+1 means one electron missing from the system,
                tot_charge=-1 means one additional electron, and so on.

                In a periodic calculation a compensating jellium background is 
                inserted to remove divergences if the cell is not neutral.
            }
        }
        
        var tot_magnetization -type REAL { 
            default { -1 [unspecified] }
            info {
                Total majority spin charge - minority spin charge.
                Used to impose a specific total electronic magnetization.
                If unspecified then tot_magnetization variable is ignored and
                the amount of electronic magnetization is determined during
                the self-consistent cycle.
            }
        }
        
        dimension starting_magnetization -start 1 -end ntyp -type REAL {
            info {
                Starting spin polarization on atomic type 'i' in a spin 
                polarized calculation. Values range between -1 (all spins
                down for the valence electrons of atom type 'i') to 1
                (all spins up). Breaks the symmetry and provides a starting
                point for self-consistency. The default value is zero, BUT a 
                value MUST be specified for AT LEAST one atomic type in spin
                polarized calculations, unless you constrain the magnetization
                (see @ref tot_magnetization and @ref constrained_magnetization).
                Note that if you start from zero initial magnetization, you 
                will invariably end up in a nonmagnetic (zero magnetization)
                state. If you want to start from an antiferromagnetic state,
                you may need to define two different atomic species
                corresponding to sublattices of the same atomic type.
                starting_magnetization is ignored if you are performing a 
                non-scf calculation, if you are restarting from a previous
                run, or restarting from an interrupted run.
                If you fix the magnetization with @ref tot_magnetization,
                you should not specify starting_magnetization.
                In the spin-orbit case starting with zero 
                starting_magnetization on all atoms imposes time reversal
                symmetry. The magnetization is never calculated and 
                kept zero (the internal variable domag is .FALSE.).
            }
        }

        var ecutwfc -type REAL {
            status { REQUIRED }
            info {
                kinetic energy cutoff (Ry) for wavefunctions
            }
        }
        
        var ecutrho -type REAL { 
            default { 4 * @ref ecutwfc }
            info {
                Kinetic energy cutoff (Ry) for charge density and potential
                For norm-conserving pseudopotential you should stick to the
                default value, you can reduce it by a little but it will 
                introduce noise especially on forces and stress.
                If there are ultrasoft PP, a larger value than the default is
                often desirable (ecutrho = 8 to 12 times @ref ecutwfc, typically).
                PAW datasets can often be used at 4*@ref ecutwfc, but it depends
                on the shape of augmentation charge: testing is mandatory.
                The use of gradient-corrected functional, especially in cells 
                with vacuum, or for pseudopotential without non-linear core
                correction, usually requires an higher values of ecutrho
                to be accurately converged.
            }
        }

        var ecutfock -type REAL { 
            default { ecutrho }
            info {
                Kinetic energy cutoff (Ry) for the exact exchange operator in 
                EXX type calculations. By default this is the same as @ref ecutrho
                but in some EXX calculations significant speed-up can be found
                by reducing ecutfock, at the expense of some loss in accuracy.
                Must be .gt. @ref ecutwfc. Not implemented for stress calculation.
                Use with care, especially in metals where it may give raise 
                to instabilities.
            }
        }
        
        vargroup -type INTEGER {
            var nr1
            var nr2
            var nr3
            info {
                Three-dimensional FFT mesh (hard grid) for charge
                density (and scf potential). If not specified
                the grid is calculated based on the cutoff for
                charge density (see also @ref ecutrho)
                Note: you must specify all three dimensions for this setting to
                be used.
            }
        }

        vargroup -type INTEGER {
            var nr1s
            var nr2s
            var nr3s
            info {
                Three-dimensional mesh for wavefunction FFT and for the smooth
                part of charge density ( smooth grid ).
                Coincides with @ref nr1, @ref nr2, @ref nr3 if @ref ecutrho = 4 * ecutwfc ( default )
                Note: you must specify all three dimensions for this setting to
                be used.
            }
        }
        
        var nosym -type LOGICAL { 
            default { .FALSE. }
            info {
                if (.TRUE.) symmetry is not used, which means that:
                
                - if a list of k points is provided in input, it is used
                  "as is": symmetry-inequivalent k-points are not generated,
                  and the charge density is not symmetrized;

                - if a uniform (Monkhorst-Pack) k-point grid is provided in 
                  input, it is expanded to cover the entire Brillouin Zone,
                  irrespective of the crystal symmetry. 
                  Time reversal symmetry is assumed so k and -k are considered
                  as equivalent unless @ref noinv=.true. is specified.

                A careful usage of this option can be advantageous:
                - in low-symmetry large cells, if you cannot afford a k-point
                  grid with the correct symmetry
                - in MD simulations
                - in calculations for isolated atoms
            }
        }

        var nosym_evc -type LOGICAL { 
            default { .FALSE. }
            info {
                if (.TRUE.) symmetry is not used, and k points are 
                forced to have the symmetry of the Bravais lattice; 
                an automatically generated Monkhorst-Pack grid will contain
                all points of the grid over the entire Brillouin Zone,
                plus the points rotated by the symmetries of the Bravais 
                lattice which were not in the original grid. The same 
                applies if a k-point list is provided in input instead
                of a Monkhorst-Pack grid. Time reversal symmetry is assumed
                so k and -k are equivalent unless @ref noinv=.true. is specified.
                This option differs from @ref nosym because it forces k-points
                in all cases to have the full symmetry of the Bravais lattice
                (not all uniform grids have such property!)
            }
        }

        var noinv -type LOGICAL { 
            default { .FALSE. }
            info {
                if (.TRUE.) disable the usage of k => -k symmetry 
                (time reversal) in k-point generation
            }
        }

        var no_t_rev -type LOGICAL { 
            default { .FALSE. }
            info {
                if (.TRUE.) disable the usage of magnetic symmetry operations
                that consist in a rotation + time reversal. 
            }
        }

       var force_symmorphic -type LOGICAL { 
           default { .FALSE. }
           info {
               if (.TRUE.) force the symmetry group to be symmorphic by disabling
               symmetry operations having an associated fractionary translation
          }
      }

       var use_all_frac -type LOGICAL { 
           default { .FALSE. }
           info {
               if (.TRUE.) do not discard symmetry operations with an
               associated fractionary translation that does not send the
               real-space FFT grid into itself. These operations are 
               incompatible with real-space symmetrization but not with the
               new G-space symmetrization. BEWARE: do not use for phonons
               and for hybrid functionals! Both still use symmetrization
               in real space.
          }
      }

        var occupations -type CHARACTER {
            options {
                info { Available options are: }
                
                opt -val 'smearing' {
                    gaussian smearing for metals; 
                    see variables @ref smearing and @ref degauss
                }
                opt -val 'tetrahedra' {
                    Tetrahedron method, Bloechl's version:
                    P.E. Bloechl, PRB 49, 16223 (1994)
                    Requires uniform grid of k-points, to be
                    automatically generated (see card @ref K_POINTS).
                    Well suited for calculation of DOS, 
                    less so (because not variational) for
                    force/optimization/dynamics calculations.
		}
		opt -val 'tetrahedra_lin' {
                    Original linear tetrahedron method.
                    To be used only as a reference;
                    the optimized tetrahedron method is more efficient.
                }
		opt -val 'tetrahedra_opt' {
                    Optimized tetrahedron method:
                    see M. Kawamura, PRB 89, 094515 (2014).
                    Can be used for phonon calculations as well.
                }
                opt -val 'fixed' {
                    for insulators with a gap
                }
                opt -val 'from_input' {
                    The occupation are read from input file,
                    card @ref OCCUPATIONS. Option valid only for a
                    single k-point, requires @ref nbnd to be set 
                    in input. Occupations should be consistent 
                    with the value of @ref tot_charge.
                }
            }
        }

        var one_atom_occupations -type LOGICAL { 
            default { .FALSE. }
            info {
               This flag is used for isolated atoms (@ref nat=1) together with 
               @ref occupations='from_input'. If it is .TRUE., the wavefunctions 
               are ordered as the atomic starting wavefunctions, independently 
               from their eigenvalue. The occupations indicate which atomic 
               states are filled.
                
               The order of the states is written inside the UPF pseudopotential file.
               In the scalar relativistic case: 
               S -> l=0, m=0 
               P -> l=1, z, x, y
               D -> l=2, r^2-3z^2, xz, yz, xy, x^2-y^2

               In the noncollinear magnetic case (with or without spin-orbit), 
               each group of states is doubled. For instance:
               P -> l=1, z, x, y for spin up, l=1, z, x, y for spin down.
               Up and down is relative to the direction of the starting
               magnetization.
                
               In the case with spin-orbit and time-reversal 
               (@ref starting_magnetization=0.0) the atomic wavefunctions are 
               radial functions multiplied by spin-angle functions.
               For instance:
               P -> l=1, j=1/2, m_j=-1/2,1/2. l=1, j=3/2, 
                    m_j=-3/2, -1/2, 1/2, 3/2.

               In the magnetic case with spin-orbit the atomic wavefunctions
               can be forced to be spin-angle functions by setting
               @ref starting_spin_angle to .TRUE..
            }
        }

        var starting_spin_angle -type LOGICAL { 
            default { .FALSE. }
            info {
               In the spin-orbit case when @ref domag=.TRUE., by default,
               the starting wavefunctions are initialized as in scalar 
               relativistic noncollinear case without spin-orbit.

               By setting @ref starting_spin_angle=.TRUE. this behaviour can
               be changed and the initial wavefunctions are radial 
               functions multiplied by spin-angle functions. 

               When @ref domag=.FALSE. the initial wavefunctions are always
               radial functions multiplied by spin-angle functions 
               independently from this flag.

               When @ref lspinorb is .FALSE. this flag is not used.
            }
        }

        var degauss -type REAL { 
            default { 0.D0 Ry }
            info {
                value of the gaussian spreading (Ry) for brillouin-zone
                integration in metals.
            }
        }
        
        var smearing -type CHARACTER {
            default { 'gaussian' }

            options {
                info {
                    Available options are:
                }
                
                opt -val {'gaussian', 'gauss'} {
                    ordinary Gaussian spreading (Default)
                }
                    
                opt -val {'methfessel-paxton', 'm-p', 'mp'} {
                    Methfessel-Paxton first-order spreading
                    (see PRB 40, 3616 (1989)).
                }

                opt -val {'marzari-vanderbilt', 'cold', 'm-v', 'mv'} {
                    Marzari-Vanderbilt cold smearing
                    (see PRL 82, 3296 (1999))
                }
                    
                opt -val {'fermi-dirac', 'f-d', 'fd'} {
                    smearing with Fermi-Dirac function
                }
            }
        }
        
        var nspin -type INTEGER {
            default { 1 }
            info {
                nspin = 1 :  non-polarized calculation (default)
                
                nspin = 2 :  spin-polarized calculation, LSDA
                             (magnetization along z axis)

                nspin = 4 :  spin-polarized calculation, noncollinear
                             (magnetization in generic direction)
                             DO NOT specify @ref nspin in this case;
                             specify @ref noncolin=.TRUE. instead
            }
        }

        var noncolin -type LOGICAL {
            default { .false. }
            info {
                if .true. the program will perform a noncollinear calculation.
            }
        }
        
        var ecfixed -type REAL { default { 0.0 }; see { q2sigma } }         
        var qcutz   -type REAL { default { 0.0 }; see { q2sigma } }         
        var q2sigma -type REAL { 
            default { 0.1 } 
            info { 
                ecfixed, qcutz, q2sigma:  parameters for modified functional to be 
                used in variable-cell molecular dynamics (or in stress calculation).
                "ecfixed" is the value (in Rydberg) of the constant-cutoff;
                "qcutz" and "q2sigma" are the height and the width (in Rydberg)
                of the energy step for reciprocal vectors whose square modulus
                is greater than "ecfixed". In the kinetic energy, G^2 is
                replaced by G^2 + qcutz * (1 + erf ( (G^2 - ecfixed)/q2sigma) )
                See: M. Bernasconi et al, J. Phys. Chem. Solids 56, 501 (1995),
		doi:10.1016/0022-3697(94)00228-2
            }
        }
        
        var input_dft -type CHARACTER {
            default { read from pseudopotential files } 
            info {
                   Exchange-correlation functional: eg 'PBE', 'BLYP' etc
                   See Modules/funct.f90 for allowed values. 
                   Overrides the value read from pseudopotential files.
                   Use with care and if you know what you are doing!
            }
        }

        var exx_fraction -type REAL { 
            default { it depends on the specified functional }
            info {
                Fraction of EXX for hybrid functional calculations. In the case of 
                @ref input_dft='PBE0', the default value is 0.25, while for @ref input_dft='B3LYP'
                the @ref exx_fraction default value is 0.20.
            }
        }

        var screening_parameter -type REAL {
            default {0.106}
            info {
                screening_parameter for HSE like hybrid functionals. 
                For more information, see:
		J. Chem. Phys. 118, 8207 (2003), doi:10.1063/1.1564060
                J. Chem. Phys. 124, 219906 (2006), doi:10.1063/1.2204597
            }
        }


        var exxdiv_treatment -type CHARACTER {
            default {'gygi-baldereschi'}
            options {
                info {
                    Specific for EXX. It selects the kind of approach to be used
                    for treating the Coulomb potential divergencies at small q vectors.
                }

                opt -val 'gygi-baldereschi' { appropriate for cubic and quasi-cubic supercells }
                
                opt -val 'vcut_spherical' { appropriate for cubic and quasi-cubic supercells }

                opt -val 'vcut_ws' { appropriate for strongly anisotropic supercells, see also @ref ecutvcut. }
                
                opt -val 'none' { sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE) }
            }
        }

        var x_gamma_extrapolation -type LOGICAL {
            default {.true.}
            info {
                Specific for EXX. If .true., extrapolate the G=0 term of the
                potential (see README in examples/EXX_example for more)
                Set this to .false. for GAU-PBE.
            }
         }

        var ecutvcut -type REAL {
            default { 0.0 Ry }
            see { exxdiv_treatment } 
            info {
                Reciprocal space cutoff for correcting Coulomb potential
                divergencies at small q vectors.
            }
        }
	
        vargroup -type INTEGER {
            var nqx1
            var nqx2
            var nqx3
            info {
                Three-dimensional mesh for q (k1-k2) sampling of 
                the Fock operator (EXX). Can be smaller than 
                the number of k-points.

                Currently this defaults to the size of the k-point mesh used.
                In QE =< 5.0.2 it defaulted to nqx1=nqx2=nqx3=1.
            }
        }

        var lda_plus_u -type LOGICAL { 
            default { .FALSE. }
            status {
                DFT+U (formerly known as LDA+U) currently works only for 
                a few selected elements. Modify @tt Modules/set_hubbard_l.f90 and 
                @tt PW/src/tabd.f90 if you plan to use DFT+U with an element that 
                is not configured there.
            }
            info { 
                Specify @ref lda_plus_u = .TRUE. to enable DFT+U calculations
                See: Anisimov, Zaanen, and Andersen, PRB 44, 943 (1991); 
                     Anisimov et al., PRB 48, 16929 (1993); 
                     Liechtenstein, Anisimov, and Zaanen, PRB 52, R5467 (1994).
                You must specify, for each species with a U term, the value of
                U and (optionally) alpha, J of the Hubbard model (all in eV):
                see @ref lda_plus_u_kind, @ref Hubbard_U, @ref Hubbard_alpha, @ref Hubbard_J
            }
        }
        var lda_plus_u_kind -type INTEGER { 
            default { 0 }
            info {
                Specifies the type of DFT+U calculation:
                
                   0   simplified version of Cococcioni and de Gironcoli, 
                       PRB 71, 035105 (2005), using @ref Hubbard_U
                
                   1   rotationally invariant scheme of Liechtenstein et al., 
                       using @ref Hubbard_U and @ref Hubbard_J
            }
        }
        dimension Hubbard_U -start 1 -end ntyp -type REAL {      
            default { 0.D0 for all species }
            info {
                Hubbard_U(i): U parameter (eV) for species i, DFT+U calculation 
            }
        }
        dimension Hubbard_J0 -start 1 -end ntype -type REAL {
            default { 0.D0 for all species }
            info {
                Hubbard_J0(i): J0 parameter (eV) for species i, DFT+U+J calculation,
                see PRB 84, 115108 (2011) for details.
            }
        } 
        dimension Hubbard_alpha -start 1 -end ntyp -type REAL { 
            default { 0.D0 for all species }
            info {
                Hubbard_alpha(i) is the perturbation (on atom i, in eV)
                used to compute U with the linear-response method of
                Cococcioni and de Gironcoli, PRB 71, 35105 (2005)
                (only for @ref lda_plus_u_kind=0)
            }
        }
        dimension Hubbard_beta -start 1 -end ntyp -type REAL { 
            default { 0.D0 for all species }
            info {
                Hubbard_beta(i) is the perturbation (on atom i, in eV)
                used to compute J0 with the linear-response method of
                Cococcioni and de Gironcoli, PRB 71, 35105 (2005)
                (only for @ref lda_plus_u_kind=0). See also 
                PRB 84, 115108 (2011).
            }
        }
        var Hubbard_J(i,ityp) { 
            default { 0.D0 for all species }
            info {
                Hubbard_J(i,ityp): J parameters (eV) for species ityp, 
                used in DFT+U calculations (only for @ref lda_plus_u_kind=1)
                For p orbitals:  J = Hubbard_J(1,ityp);
                For d orbitals:  J = Hubbard_J(1,ityp), B = Hubbard_J(2,ityp);
                For f orbitals:  J = Hubbard_J(1,ityp), E2 = Hubbard_J(2,ityp),
                                 E3= Hubbard_J(3,ityp).
                If B or E2 or E3 are not specified or set to 0 they will be
                calculated from J using atomic ratios.
            }
        }
        
        var starting_ns_eigenvalue(m,ispin,I) -type REAL { 
            default { -1.d0 that means NOT SET }
            info {
                In the first iteration of an DFT+U run it overwrites
                the m-th eigenvalue of the ns occupation matrix for the
                ispin component of atomic species I. Leave unchanged
                eigenvalues that are not set. This is useful to suggest
                the desired orbital occupations when the default choice
                takes another path.
            }
        }

        var U_projection_type -type CHARACTER {   
            default { 'atomic' }
            options {
                info {
                    Only active when @ref lda_plus_U is .true., specifies the type
                    of projector on localized orbital to be used in the DFT+U
                    scheme.
                    
                    Currently available choices:
                }
                
                opt -val 'atomic' { use atomic wfc's (as they are) to build the projector }

                opt -val 'ortho-atomic' { use Lowdin orthogonalized atomic wfc's }
                
                opt -val 'norm-atomic' {
                    Lowdin normalization of atomic wfc. Keep in mind:
                    atomic wfc are not orthogonalized in this case.
                    This is a "quick and dirty" trick to be used when
                    atomic wfc from the pseudopotential are not
                    normalized (and thus produce occupation whose
                    value exceeds unity). If orthogonalized wfc are
                    not needed always try @b 'atomic' first.
                }
                opt -val 'file' {
                    use the information from file "prefix".atwfc that must
                    have been generated previously, for instance by pmw.x
                    (see PP/src/poormanwannier.f90 for details).
                }

                opt -val 'pseudo' {
                    use the pseudopotential projectors. The charge density
                    outside the atomic core radii is excluded.
                    N.B.: for atoms with +U, a pseudopotential with the 
                    all-electron atomic wavefunctions is required (i.e.,
                    as generated by ld1.x with lsave_wfc flag).
                }

                info {
                    NB: forces and stress currently implemented only for the
                    'atomic' and 'pseudo' choice.
                }
            }
        }

        var edir -type INTEGER {
            info {
                The direction of the electric field or dipole correction is
                parallel to the bg(:,edir) reciprocal lattice vector, so the
                potential is constant in planes defined by FFT grid points;
                @ref edir = 1, 2 or 3. Used only if @ref tefield is .TRUE.
            }
        }
        
        var emaxpos -type REAL { 
            default { 0.5D0 }
            info {
                Position of the maximum of the saw-like potential along crystal
                axis @ref edir, within the  unit cell (see below), 0 < emaxpos < 1
                Used only if @ref tefield is .TRUE.
            }
        }
        
        var eopreg -type REAL {
            default { 0.1D0 }
            info {
                Zone in the unit cell where the saw-like potential decreases.
                ( see below, 0 < eopreg < 1 ). Used only if @ref tefield is .TRUE.
            }
        }

        var eamp -type REAL { 
            default { 0.001 a.u. }
            info {
                Amplitude of the electric field, in ***Hartree*** a.u.;
                1 a.u. = 51.4220632*10^10 V/m. Used only if @ref tefield==.TRUE.
                The saw-like potential increases with slope @ref eamp in the
                region from (@ref emaxpos+@ref eopreg-1) to (@ref emaxpos), then decreases
                to 0 until (@ref emaxpos+@ref eopreg), in units of the crystal
                vector @ref edir. Important: the change of slope of this
                potential must be located in the empty region, or else
                unphysical forces will result.
            }
        }
    
	dimension angle1 -start 1 -end ntyp -type REAL {
            info {
                The angle expressed in degrees between the initial
                magnetization and the z-axis. For noncollinear calculations
                only; index i runs over the atom types.
            }
        }

        dimension angle2 -start 1 -end ntyp -type REAL {
            info {
                The angle expressed in degrees between the projection
                of the initial magnetization on x-y plane and the x-axis.
                For noncollinear calculations only.
            }
        }

        var constrained_magnetization -type CHARACTER { 
            see { lambda, fixed_magnetization }
            default { 'none' }
            options {
                info {
                    Used to perform constrained calculations in magnetic systems.
                    Currently available choices:
                }

                opt -val 'none' {
                         no constraint
                }
                
                opt -val 'total' {
                         total magnetization is constrained by
                         adding a penalty functional to the total energy:
                    
                         LAMBDA * SUM_{i} ( magnetization(i) - fixed_magnetization(i) )**2
                        
                         where the sum over i runs over the three components of
                         the magnetization. Lambda is a real number (see below).
                         Noncolinear case only. Use @ref tot_magnetization for LSDA
                }
                
                opt -val 'atomic' {
                         atomic magnetization are constrained to the defined
                         starting magnetization adding a penalty:

                         LAMBDA * SUM_{i,itype} ( magnetic_moment(i,itype) - mcons(i,itype) )**2
                        
                         where i runs over the cartesian components (or just z 
                         in the collinear case) and itype over the types (1-ntype).
                         mcons(:,:) array is defined from starting_magnetization,
                         (and angle1, angle2 in the non-collinear case). lambda is 
                         a real number
                }
                opt -val {'total direction'} {
                          the angle theta of the total magnetization
                          with the z axis (theta = fixed_magnetization(3))  
                          is constrained: 

                          LAMBDA * ( arccos(magnetization(3)/mag_tot) - theta )**2

                          where mag_tot is the modulus of the total magnetization.
                }
                opt -val {'atomic direction'} {
                          not all the components of the atomic
                          magnetic moment are constrained but only the cosine
                          of angle1, and the penalty functional is:

                          LAMBDA * SUM_{itype} ( mag_mom(3,itype)/mag_mom_tot - cos(angle1(ityp)) )**2
                }
                info {
                    N.B.: symmetrization may prevent to reach the desired orientation
                    of the magnetization. Try not to start with very highly symmetric
                    configurations or use the nosym flag (only as a last remedy)
                }
            }
        }
        
        dimension fixed_magnetization -start 1 -end 3 -type REAL { 
            see { constrained_magnetization }
            default { 0.d0 }
            info {
                total magnetization vector (x,y,z components) to be kept
                fixed when @ref constrained_magnetization=='total'
            }
        }
        
        var lambda -type REAL {
            see { constrained_magnetization }
            default { 1.d0 }
            info {
                parameter used for constrained_magnetization calculations
                N.B.: if the scf calculation does not converge, try to reduce lambda 
                      to obtain convergence, then restart the run with a larger lambda
            }
        }
        
        var report -type INTEGER {
            default { 100 }
            info {
                Number of iterations after which the program
                writes all the atomic magnetic moments.
            }
        }
        
        var lspinorb -type LOGICAL {
            info {
                if .TRUE. the noncollinear code can use a pseudopotential with
                spin-orbit.
            }
        }
        
        var assume_isolated -type CHARACTER { 
            default { 'none' }
            options {
                info { 
                    Used to perform calculation assuming the system to be
                    isolated (a molecule or a cluster in a 3D supercell).
                    
                    Currently available choices:
                }

                opt -val 'none' {
                    (default): regular periodic calculation w/o any correction.
                }
                opt -val {'makov-payne', 'm-p', 'mp'} {
                    the Makov-Payne correction to the 
                    total energy is computed. An estimate of the vacuum 
                    level is also calculated so that eigenvalues can be 
                    properly aligned. ONLY FOR CUBIC SYSTEMS (@ref ibrav=1,2,3).
                    Theory: G.Makov, and M.C.Payne, 
                         "Periodic boundary conditions in ab initio
                         calculations" , PRB 51, 4014 (1995).
                }

                opt -val {'martyna-tuckerman', 'm-t', 'mt'} {
                    Martyna-Tuckerman correction
                    to both total energy and scf potential. Adapted from:
                    G.J. Martyna, and M.E. Tuckerman,
                    "A reciprocal space based method for treating long
                    range interactions in ab-initio and force-field-based
                    calculation in clusters", J. Chem. Phys. 110, 2810 (1999),
		    doi:10.1063/1.477923.
                }

                opt -val 'esm' {
                    Effective Screening Medium Method.
                    For polarized or charged slab calculation, embeds
                    the simulation cell within an effective semi-
                    infinite medium in the perpendicular direction
                    (along z). Embedding regions can be vacuum or
                    semi-infinite metal electrodes (use @ref esm_bc to
                    choose boundary conditions). If between two
                    electrodes, an optional electric field
                    ('esm_efield') may be applied. Method described in
                    M. Otani and O. Sugino, "First-principles calculations 
                    of charged surfaces and interfaces: A plane-wave 
                    nonrepeated slab approach", PRB 73, 115407 (2006).

		    NB:
                       - Two dimensional (xy plane) average charge density
                         and electrostatic potentials are printed out to
                         'prefix.esm1'.                  
                    
                       - Requires cell with a_3 lattice vector along z,
                         normal to the xy plane, with the slab centered
                         around z=0. Also requires symmetry checking to be
                         disabled along z, either by setting @ref nosym = .TRUE.
                         or by very slight displacement (i.e., 5e-4 a.u.)
                         of the slab along z.
                       
                    See @ref esm_bc, @ref esm_efield, @ref esm_w, @ref esm_nfit.
                }
            }
        }

        var esm_bc -type CHARACTER {
            see { assume_isolated }
            default { 'pbc' }
            options {
                info {
                    If @ref assume_isolated = 'esm', determines the boundary
                    conditions used for either side of the slab.
                    
                    Currently available choices:
                }

                opt -val 'pbc' { (default): regular periodic calculation (no ESM). }

                opt -val 'bc1' { Vacuum-slab-vacuum (open boundary conditions). }

                opt -val 'bc2' {
                    Metal-slab-metal (dual electrode configuration).
                    See also @ref esm_efield.
                }
                opt -val 'bc3' { Vacuum-slab-metal }
            }
        }

        var esm_w -type REAL {
            see { assume_isolated }
            default { 0.d0 }
            info {
                If @ref assume_isolated = 'esm', determines the position offset
                [in a.u.] of the start of the effective screening region,
                measured relative to the cell edge. (ESM region begins at
                z = +/- [L_z/2 + esm_w] ).
            }
        }

        var esm_efield -type REAL {
            see { assume_isolated }
            default { 0.d0 }
            info {
                If @ref assume_isolated = 'esm' and @ref esm_bc = 'bc2', gives the
                magnitude of the electric field [Ry/a.u.] to be applied
                between semi-infinite ESM electrodes.
            }
        }

        var esm_nfit -type INTEGER {
            see { assume_isolated }
            default { 4 }
            info {
                If @ref assume_isolated = 'esm', gives the number of z-grid points
                for the polynomial fit along the cell edge.
            }
        }

        var fcp_mu -type REAL {
            see { lfcpopt }
            default { 0.d0 }
            info {
                If @ref lfcpopt = .TRUE., gives the target Fermi energy [Ry]. One can start 
                with appropriate total charge of the system by giving 'tot_charge'.
            }
        }

         var vdw_corr -type CHARACTER {
             default { 'none' }
             see {
                 london_s6, london_rcut, london_c6, london_rvdw, ts_vdw_econv_thr, ts_vdw_isolated, xdm_a1, xdm_a2
             }
             options {
                 info {
                     Type of Van der Waals correction. Allowed values:
                 }

                 opt -val {'grimme-d2', 'Grimme-D2', 'DFT-D', 'dft-d' } {
                     Semiempirical Grimme's DFT-D2.
                     Optional variables: @ref london_s6, @ref london_rcut, @ref london_c6, @ref london_rvdw,
                     S. Grimme, J. Comp. Chem. 27, 1787 (2006), doi:10.1002/jcc.20495
                     V. Barone et al., J. Comp. Chem. 30, 934 (2009), doi:10.1002/jcc.21112
                 }

                 opt -val {'TS', 'ts', 'ts-vdw', 'ts-vdW', 'tkatchenko-scheffler'} {
                     Tkatchenko-Scheffler dispersion corrections with first-principle derived
                     C6 coefficients (implemented in CP only).
                     Optional variables: @ref ts_vdw_econv_thr, @ref ts_vdw_isolated
                     See A. Tkatchenko and M. Scheffler, PRL 102, 073005 (2009).
                 }

                 opt -val {'XDM', 'xdm'} {
                     Exchange-hole dipole-moment model. Optional variables: @ref xdm_a1, @ref xdm_a2
                     A. D. Becke et al., J. Chem. Phys. 127, 154108 (2007), doi:10.1063/1.2795701
                     A. Otero de la Roza et al., J. Chem. Phys. 136, 174109 (2012),
		     doi:10.1063/1.4705760
                 }
                 info { Note that non-local functionals (eg vdw-DF) are NOT specified here but in @ref input_dft }
             }
         }

         var london -type LOGICAL {
           default { .FALSE. }
           status {
               OBSOLESCENT, same as @ref vdw_corr='DFT-D'
           }
         }

         var london_s6 -type REAL {
           default { 0.75 }
           info {
               global scaling parameter for DFT-D. Default is good for PBE.
           }
         }
         dimension london_c6 -type REAL -start 1 -end ntyp {
           default { standard Grimme-D2 values }
           info {
               atomic C6 coefficient of each atom type

               ( if not specified default values from S. Grimme, J. Comp. Chem. 27, 1787 (2006),
		 doi:10.1002/jcc.20495 are used; see file Modules/mm_dispersion.f90 )
           }
         }
         dimension london_rvdw -type REAL -start 1 -end ntyp {
           default { standard Grimme-D2 values }
           info {
               atomic vdw radii of each atom type

               ( if not specified default values from S. Grimme, J. Comp. Chem. 27, 1787 (2006),
		 doi:10.1002/jcc.20495 are used; see file Modules/mm_dispersion.f90 )
           }
         }
         var london_rcut -type REAL {
           default { 200 }
           info {
               cutoff radius (a.u.) for dispersion interactions
           }
         }
        var ts_vdw_econv_thr -type REAL {
          default { 1.D-6 }
          info {
             Optional: controls the convergence of the vdW energy (and forces). The default value
             is a safe choice, likely too safe, but you do not gain much in increasing it
          }
        }

        var ts_vdw_isolated -type LOGICAL {
          default { .FALSE. }
          info {
             Optional: set it to .TRUE. when computing the Tkatchenko-Scheffler vdW energy
             for an isolated (non-periodic) system.
          }
        }

         var xdm -type LOGICAL {
             default { .FALSE. }
             status {
               OBSOLESCENT, same as @ref vdw_corr='xdm'
             }
         }

         var xdm_a1 -type REAL {
           default { 0.6836 }
           info {
               Damping function parameter a1 (adimensional). This value should change
               with the exchange-correlation functional. The default corresponds to 
               PW86PBE. 
               For other functionals, see:
                  http://schooner.chem.dal.ca/wiki/XDM
	          A. Otero de la Roza, E. R. Johnson, J. Chem. Phys. 138, 204109 (2013),
	          doi:10.1063/1.4705760
           }
         }
         var xdm_a2 -type REAL {
           default { 1.5045 }
           info {
               Damping function parameter a2 (angstrom). This value should change
               with the exchange-correlation functional. The default corresponds to 
               PW86PBE. 
               For other functionals, see:
                  http://schooner.chem.dal.ca/wiki/XDM
	          A. Otero de la Roza, E. R. Johnson, J. Chem. Phys. 138, 204109 (2013),
	          doi:10.1063/1.4705760
           }
         }

         var space_group -type INTEGER {
             default { 0 }
             info {
                 The number of the space group of the crystal, as given
                 in the International Tables of Crystallography A (ITA).
                 This allows to give in input only the inequivalent atomic 
                 positions. The positions of all the symmetry equivalent atoms
                 are calculated by the code. Used only when the atomic positions
                 are of type crystal_sg. 
             }
         }

         var uniqueb -type LOGICAL {
             default { .FALSE. }
             info {
                  Used only for monoclinic lattices. If .TRUE. the b
                  unique ibrav (-12 or -13) are used, and symmetry 
                  equivalent positions are chosen assuming that the
                  two fold axis or the mirror normal is parallel to the
                  b axis. If .FALSE. it is parallel to the c axis.
             }
         }

         var origin_choice -type INTEGER {
             default { 1 }
             info {
                  Used only for space groups that in the ITA allow 
                  the use of two different origins. origin_choice=1,
                  means the first origin, while origin_choice=2 is the
                  second origin.
             }
         }
    
         var rhombohedral -type LOGICAL {
             default { .TRUE. }
             info {
                  Used only for rhombohedral space groups. 
                  When .TRUE. the coordinates of the inequivalent atoms are
                  given with respect to the rhombohedral axes, when .FALSE.
                  the coordinates of the inequivalent atoms are given with
                  respect to the hexagonal axes. They are converted internally
                  to the rhombohedral axes and @ref ibrav=5 is used in both cases.
             }
         }
    
        group {
	    label { below variables are used only if @ref monopole = .TRUE. }

	    var zmon -type REAL {
		default { 0.5 }
		info {
		    used only if @ref monopole = .TRUE.
		    Specifies the position of the charged plate which represents
		    the counter charge in doped systems (@ref tot_charge .ne. 0).
		    In units of the unit cell length in @i z direction, @ref zmon in ]0,1[
                    Details of the monopole potential can be found in
                    T. Brumme, M. Calandra, F. Mauri; PRB 89, 245406 (2014).
		}
	    }

	    var realxz -type LOGICAL {
		default { .FALSE. }
		info {
		    used only if @ref monopole = .TRUE.
		    Allows the relaxation of the system towards the charged plate.
		    Use carefully and utilize either a layer of fixed atoms or a
		    potential barrier (@ref block=.TRUE.) to avoid the atoms moving to
		    the position of the plate or the dipole of the dipole
		    correction (@ref dipfield=.TRUE.).
		}
	    }

	    var block -type LOGICAL {
		default { .FALSE. }
		info {
		    used only if @ref monopole = .TRUE.
		    Adds a potential barrier to the total potential seen by the
		    electrons to mimic a dielectric in field effect configuration
		    and/or to avoid electrons spilling into the vacuum region for
		    electron doping. Potential barrier is from @ref block_1 to @ref block_2 and
		    has a height of block_height.
		    If @ref dipfield = .TRUE. then @ref eopreg is used for a smooth increase and
		    decrease of the potential barrier.
		}
	    }

	    var block_1 -type REAL {
		default { 0.45 }
		info {
		    used only if @ref monopole = .TRUE. and @ref block = .TRUE.
		    lower beginning of the potential barrier, in units of the
		    unit cell size along @i z, @ref block_1 in ]0,1[
		}
	    }

	    var block_2 -type REAL {
		default { 0.55 }
		info {
		    used only if @ref monopole = .TRUE. and @ref block = .TRUE.
		    upper beginning of the potential barrier, in units of the
		    unit cell size along @i z, @ref block_2 in ]0,1[
                }
	    }

	    var block_height -type REAL {
		default { 0.1 }
		info {
		    used only if @ref monopole = .TRUE. and @ref block = .TRUE.
		    Height of the potential barrier in Rydberg.
		}
	    }
	}

    }

    #
    # namelist ELECTRONS
    #

    namelist ELECTRONS {

        var electron_maxstep    -type INTEGER { 
            default { 100 }
            info {
                maximum number of iterations in a scf step
            }
        }

        var scf_must_converge   -type LOGICAL { 
            default { .TRUE. }
            info {
                If .false. do not stop molecular dynamics or ionic relaxation
                when electron_maxstep is reached. Use with care.
            }
        }


        var conv_thr -type REAL { 
            default { 1.D-6 }
            info {
                Convergence threshold for selfconsistency:
                   estimated energy error < conv_thr
                (note that conv_thr is extensive, like the total energy).
                
                For non-self-consistent calculations, conv_thr is used
                to set the default value of the threshold (ethr) for
                iterative diagonalizazion: see @ref diago_thr_init
            }
        }
        
        var adaptive_thr -type LOGICAL { 
            default { .FALSE }
            info {
                If .TRUE. this turns on the use of an adaptive @ref conv_thr for 
                the inner scf loops when using EXX.
            }
        }

        var conv_thr_init -type REAL { 
            default { 1.D-3 }
            info {
                When @ref adaptive_thr = .TRUE. this is the convergence threshold 
                used for the first scf cycle.           
            }
        }
        
        var conv_thr_multi -type REAL { 
            default { 1.D-1 }
            info {
                When @ref adaptive_thr = .TRUE. the convergence threshold for 
                each scf cycle is given by:
                max( @ref conv_thr, @ref conv_thr_multi * dexx )
            }
        }

        var mixing_mode -type CHARACTER {
            default { 'plain' }
            options {
                info { Available options are: }
                
                opt -val 'plain' { charge density Broyden mixing }
                
                opt -val 'TF' {
                    as above, with simple Thomas-Fermi screening
                    (for highly homogeneous systems)
                }                
                opt -val 'local-TF' {
                    as above, with local-density-dependent TF screening
                    (for highly inhomogeneous systems)
                }
            }
        }

        var mixing_beta -type REAL { 
            default { 0.7D0 }
            info {
                mixing factor for self-consistency
            }
        }

        var mixing_ndim -type INTEGER { 
            default { 8 }
            info {
                number of iterations used in mixing scheme.
                If you are tight with memory, you may reduce it to 4 or so.
            }
        }

        var mixing_fixed_ns -type INTEGER { 
            default { 0 }
            info {
                For DFT+U : number of iterations with fixed ns ( ns is the
                atomic density appearing in the Hubbard term ).
            }
        }
        
        var diagonalization -type CHARACTER {
            default { 'david' }
            options {
                info { Available options are: }
                
                opt -val 'david' {
                    Davidson iterative diagonalization with overlap matrix
                    (default). Fast, may in some rare cases fail.
                }

                opt -val 'cg' {
                    Conjugate-gradient-like band-by-band diagonalization.
                    Typically slower than 'david' but it uses less memory
                    and is more robust (it seldom fails).
                }

                opt -val {'cg-serial', 'david-serial'} {
                    OBSOLETE, use @b {-ndiag 1} instead.
                    The subspace diagonalization in Davidson is performed
                    by a fully distributed-memory parallel algorithm on
                    4 or more processors, by default. The allocated memory
                    scales down with the number of procs. Procs involved 
                    in diagonalization can be changed with command-line
                    option @b -ndiag @i N. On multicore CPUs it is often
                    convenient to let just one core per CPU to work 
                    on linear algebra.
                }
            }
        }

        var ortho_para -type INTEGER { 
            default { 0 }
            status { OBSOLETE: use command-line option @tt {"-ndiag XX"} instead  }
        }

        var diago_thr_init -type REAL {
            info {
                Convergence threshold (ethr) for iterative diagonalization
                (the check is on eigenvalue convergence).
                
                For scf calculations: default is 1.D-2 if starting from a
                superposition of atomic orbitals; 1.D-5 if starting from a
                charge density. During self consistency the threshold
                is automatically reduced (but never below 1.D-13) when 
                approaching convergence.

                For non-scf calculations: default is (@ref conv_thr/N elec)/10.
            }
        }

        var diago_cg_maxiter -type INTEGER {
            info {
                For conjugate gradient diagonalization:  max number of iterations
            }
        }

        var diago_david_ndim -type INTEGER { 
            default { 4 }
            info {
                For Davidson diagonalization: dimension of workspace
                (number of wavefunction packets, at least 2 needed).
                A larger value may yield a smaller number of iterations in
                the algorithm but uses more memory and more CPU time in 
                subspace diagonalization.
                Try @ref diago_david_ndim=2 if you are tight on memory or if
                the time spent in subspace diagonalization (cdiaghg/rdiaghg)
                is significant compared to the time spent in h_psi
            }
        }

        var diago_full_acc -type LOGICAL { 
            default { .FALSE. }
            info {
                If .TRUE. all the empty states are diagonalized at the same level
                of accuracy of the occupied ones. Otherwise the empty states are
                diagonalized using a larger threshold (this should not affect
                total energy, forces, and other ground-state properties).
            }
        }

        var efield -type REAL {
            default { 0.D0 }
            info {
                Amplitude of the finite electric field (in Ry a.u.;
                1 a.u. = 36.3609*10^10 V/m). Used only if @ref lelfield==.TRUE.
                and if k-points (@ref K_POINTS card) are not automatic.
            }
        }

        dimension efield_cart -start 1 -end 3 -type REAL { 
            default { (0.D0, 0.D0, 0.D0) }
            info {
                Finite electric field (in Ry a.u.=36.3609*10^10 V/m) in
                cartesian axis. Used only if @ref lelfield==.TRUE. and if
                k-points (@ref K_POINTS card) are automatic.
            }
        }

        var efield_phase -type CHARACTER {
            default { 'none' }
            options {
                info { Available options are: }
                
                opt -val 'read' {
                    set the zero of the electronic polarization (with @ref lelfield==.true..) 
                    to the result of a previous calculation
                }                
                opt -val 'write' {
                    write on disk data on electronic polarization to be read in another 
                    calculation
                }                
                opt -val 'none' {
                    none of the above points
                }
            }  
        }
        
        var startingpot -type CHARACTER {
            options {
                info { Available options are: }
                
                opt -val 'atomic' {
                    starting potential from atomic charge superposition
                    (default for scf, *relax, *md)
                }

                opt -val 'file'  {
                    start from existing "charge-density.xml" file in the
                    directory specified by variables @ref prefix and @ref outdir
                    For nscf and bands calculation this is the default
                    and the only sensible possibility.
                }
            }
        }

        var startingwfc -type CHARACTER {
            default { 'atomic+random' }
            options {
                info { Available options are: }
                
                opt -val 'atomic' {
                    Start from superposition of atomic orbitals.
                    If not enough atomic orbitals are available,
                    fill with random numbers the remaining wfcs
                    The scf typically starts better with this option,
                    but in some high-symmetry cases one can "loose" 
                    valence states, ending up in the wrong ground state.
                }
                opt -val 'atomic+random' {
                    As above, plus a superimposed "randomization"
                    of atomic orbitals. Prevents the "loss" of states 
                    mentioned above.
                }
                opt -val 'random' {
                    Start from random wfcs. Slower start of scf but safe.
                    It may also reduce memory usage in conjunction with
                    @ref diagonalization='cg'.
                }
                opt -val 'file' {
                    Start from an existing wavefunction file in the 
                    directory specified by variables @ref prefix and @ref outdir.
                }
            }
        }

        var tqr -type LOGICAL { 
            default { .FALSE. }
            info {
                If .true., use the real-space algorithm for augmentation
                charges in ultrasoft pseudopotentials.
                Must faster execution of ultrasoft-related calculations,
                but numerically less accurate than the default algorithm.
                Use with care and after testing!
            }
        }
    }

    
    #
    # NAMELIST IONS
    #
    
    namelist IONS  {
        label { 
            input this namelist only if @ref calculation == 'relax', 'md', 'vc-relax', or 'vc-md' 
        }
    
        var ion_dynamics -type CHARACTER {
	    options {
		info {
		    Specify the type of ionic dynamics.
		    
		    For different type of calculation different possibilities are
		    allowed and different default values apply:
		    
		    @b CASE ( @ref calculation == 'relax' )
		}
		opt -val 'bfgs' {
		    @b (default)  use BFGS quasi-newton algorithm,
		    based on the trust radius procedure,
		    for structural relaxation
		}
		opt -val 'damp' {
		    use damped (quick-min Verlet)
		    dynamics for structural relaxation
		    Can be used for constrained 
		    optimisation: see @ref CONSTRAINTS card
		}		
		info {
		    @b CASE ( @ref calculation == 'md' )
		}
		opt -val 'verlet' {
		    @b (default)  use Verlet algorithm to integrate
		    Newton's equation. For constrained 
		    dynamics, see @ref CONSTRAINTS card
		}
		opt -val 'langevin' {
		    ion dynamics is over-damped Langevin
                }
                opt -val 'langevin-smc' {
                    over-damped Langevin with Smart Monte Carlo:
                    see R.J. Rossky, JCP, 69, 4628 (1978), doi:10.1063/1.436415
		}
		info {
		    @b CASE ( @ref calculation == 'vc-relax' )
		}
		opt -val 'bfgs' {
		    @b (default)  use BFGS quasi-newton algorithm;
		    cell_dynamics must be 'bfgs' too
		}
		opt -val 'damp' {
		    use damped (Beeman) dynamics for
		    structural relaxation
		}
                info {
		    @b CASE ( @ref calculation == 'vc-md' )
		}
		opt -val 'beeman' {
		    @b (default)  use Beeman algorithm to integrate
		    Newton's equation
		}
            }
        }

        var ion_positions -type CHARACTER {
            default { 'default' }
            options {
		info { Available options are: }
		
                opt -val 'default' {
                    if restarting, use atomic positions read from the
                    restart file; in all other cases, use atomic
                    positions from standard input.
                }
                opt -val 'from_input' {
                    restart the simulation with atomic positions read
                    from standard input, even if restarting.
                }
            }
        }
 
        var pot_extrapolation -type CHARACTER { 
            default { 'atomic' }
            options {
                info {
                    Used to extrapolate the potential from preceding ionic steps.
                }
                opt -val 'none' { no extrapolation }

                opt -val 'atomic' {
                    extrapolate the potential as if it was a sum of
                    atomic-like orbitals
                }
                opt -val 'first_order' {
                    extrapolate the potential with first-order
                    formula
                }

                opt -val 'second_order' {
                    as above, with second order formula
                }
                info {
                    Note: 'first_order' and 'second-order' extrapolation make sense
                    only for molecular dynamics calculations
                }
            }
        }

        var wfc_extrapolation -type CHARACTER { 
            default { 'none' }
            options {
                info {
                    Used to extrapolate the wavefunctions from preceding ionic steps.
                }
                opt -val 'none' {  no extrapolation }

                opt -val 'first_order' {
                    extrapolate the wave-functions with first-order formula.
                }

                opt -val 'second_order' {
                    as above, with second order formula.
                }
                info {
                    Note: @b 'first_order' and @b 'second-order' extrapolation make sense
                    only for molecular dynamics calculations
                }
            }
        }

        var remove_rigid_rot -type LOGICAL { 
            default { .FALSE. }
            info {
               This keyword is useful when simulating the dynamics and/or the
               thermodynamics of an isolated system. If set to true the total
               torque of the internal forces is set to zero by adding new forces
               that compensate the spurious interaction with the periodic
               images. This allows for the use of smaller supercells.

               BEWARE: since the potential energy is no longer consistent with
               the forces (it still contains the spurious interaction with the
               repeated images), the total energy is not conserved anymore.
               However the dynamical and thermodynamical properties should be
               in closer agreement with those of an isolated system.
               Also the final energy of a structural relaxation will be higher,
               but the relaxation itself should be faster.
            }
        }
         
        group {
            label {
                variables used for molecular dynamics
            }       

            var ion_temperature -type CHARACTER {
                default { 'not_controlled' }
                options {
		    info { Available options are: }
		    
                    opt -val 'rescaling' {
                        control ionic temperature via velocity rescaling
                        (first method) see parameters @ref tempw, @ref tolp, and
                        @ref nraise (for VC-MD only). This rescaling method
                        is the only one currently implemented in VC-MD
                    }
                    opt -val 'rescale-v' {
                        control ionic temperature via velocity rescaling
                        (second method) see parameters @ref tempw and @ref nraise
                    }
                    opt -val 'rescale-T' {
                        control ionic temperature via velocity rescaling
                        (third method) see parameter @ref delta_t
                    }
                    opt -val 'reduce-T' {
                        reduce ionic temperature every @ref nraise steps
                        by the (negative) value @ref delta_t
                    }
                    opt -val 'berendsen' {
                        control ionic temperature using "soft" velocity
                        rescaling - see parameters @ref tempw and @ref nraise
                    }
                    opt -val 'andersen' {
                        control ionic temperature using Andersen thermostat
                        see parameters @ref tempw and @ref nraise
                    }
                    opt -val 'initial' {
                        initialize ion velocities to temperature @ref tempw
                        and leave uncontrolled further on
                    }
                    opt -val 'not_controlled' {
                        (default) ionic temperature is not controlled
                    }
                }
            }

            var tempw -type REAL { 
                default { 300.D0 }
                info {
                    Starting temperature (Kelvin) in MD runs
                    target temperature for most thermostats.
                }
            }

            var tolp -type REAL { 
                default { 100.D0 }
                info {
                    Tolerance for velocity rescaling. Velocities are rescaled if
                    the run-averaged and target temperature differ more than tolp.
                }
            }

            var delta_t -type REAL { 
                default { 1.D0 }
                info {
                    if @ref ion_temperature == 'rescale-T' :
                           at each step the instantaneous temperature is multiplied
                           by delta_t; this is done rescaling all the velocities.

                    if @ref ion_temperature == 'reduce-T' :
                           every 'nraise' steps the instantaneous temperature is
                           reduced by -@ref delta_t (i.e. @ref delta_t < 0 is added to T)

                    The instantaneous temperature is calculated at the end of
                    every ionic move and BEFORE rescaling. This is the temperature
                    reported in the main output.
                
                    For @ref delta_t < 0, the actual average rate of heating or cooling
                    should be roughly C*delta_t/(nraise*dt) (C=1 for an
                    ideal gas, C=0.5 for a harmonic solid, theorem of energy
                    equipartition between all quadratic degrees of freedom).
                }
            }

            var nraise -type INTEGER { 
                default { 1 }
                info {
                    if @ref ion_temperature == 'reduce-T' :
                           every @ref nraise steps the instantaneous temperature is
                           reduced by -@ref delta_t (i.e. @ref delta_t is added to the temperature)
                
                    if @ref ion_temperature == 'rescale-v' :
                           every @ref nraise steps the average temperature, computed from
                           the last @ref nraise steps, is rescaled to @ref tempw

                    if @ref ion_temperature == 'rescaling' and @ref calculation == 'vc-md' :
                           every @ref nraise steps the instantaneous temperature
                           is rescaled to @ref tempw
                    
                    if @ref ion_temperature == 'berendsen' :
                           the "rise time" parameter is given in units of the time step:
                           tau = nraise*dt, so dt/tau = 1/nraise
                    
                    if @ref ion_temperature == 'andersen' :
                           the "collision frequency" parameter is given as nu=1/tau
                           defined above, so nu*dt = 1/nraise
                }
            }

            var refold_pos -type LOGICAL { 
                default { .FALSE. }
                info {
                    This keyword applies only in the case of molecular dynamics or
                    damped dynamics. If true the ions are refolded at each step into
                    the supercell.
                }
            }
        }
    
        group {
            label {
                keywords used only in BFGS calculations
            }   

            var upscale -type REAL { 
                default { 100.D0 }
                info {
                    Max reduction factor for @ref conv_thr during structural optimization
                    @ref conv_thr is automatically reduced when the relaxation
                    approaches convergence so that forces are still accurate,
                    but @ref conv_thr will not be reduced to less that @ref conv_thr / @ref upscale.
                }
            }

            var bfgs_ndim -type INTEGER { 
                default { 1 }
                info {
                    Number of old forces and displacements vectors used in the
                    PULAY mixing of the residual vectors obtained on the basis
                    of the inverse hessian matrix given by the BFGS algorithm.
                    When @ref bfgs_ndim = 1, the standard quasi-Newton BFGS method is
                    used.
                    (bfgs only)
                }
            }

            var trust_radius_max -type REAL { 
                default { 0.8D0 }
                info {
                    Maximum ionic displacement in the structural relaxation.
                    (bfgs only)
                }
            }

            var trust_radius_min -type REAL { 
                default { 1.D-3 }
                info {
                    Minimum ionic displacement in the structural relaxation
                    BFGS is reset when @ref trust_radius < @ref trust_radius_min.
                    (bfgs only)
                }
            }

            var trust_radius_ini -type REAL { 
                default { 0.5D0 }
                info {
                    Initial ionic displacement in the structural relaxation.
                    (bfgs only)
                }
            }
        
            var w_1 -type REAL { default { 0.01D0 }; see { w_2 } }
            var w_2 -type REAL { 
                default { 0.5D0 }
                info {
                    Parameters used in line search based on the Wolfe conditions.
                    (bfgs only)
                }
            }
        }

    }

    #
    # namelist CELL
    #

    namelist CELL {
        label {
            input this namelist only if @ref calculation == 'vc-relax' or 'vc-md' 
        }

        var cell_dynamics -type CHARACTER {
	    options {
		info {
		    Specify the type of dynamics for the cell.
		    For different type of calculation different possibilities
		    are allowed and different default values apply:

		    @b CASE ( @ref calculation == 'vc-relax' )
		}
		opt -val 'none' { no dynamics }
		opt -val 'sd'   { steepest descent ( not implemented ) }
		opt -val 'damp-pr' {
		    damped (Beeman) dynamics of the Parrinello-Rahman extended lagrangian
		}
		opt -val 'damp-w' {
		    damped (Beeman) dynamics of the new Wentzcovitch extended lagrangian
		}
		opt -val 'bfgs' {
		    BFGS quasi-newton algorithm @b (default)
		    @ref ion_dynamics must be @b 'bfgs' too
		}
		info {
		    @b CASE ( @ref calculation == 'vc-md' )
		}
		opt -val 'none' { no dynamics }
		opt -val 'pr' {
		    (Beeman) molecular dynamics of the Parrinello-Rahman extended lagrangian
		}
		opt -val 'w' {
		    (Beeman) molecular dynamics of the new Wentzcovitch extended lagrangian
		}
            }
        }       

        var press -type REAL { 
            default { 0.D0 }
            info { 
                Target pressure [KBar] in a variable-cell md or relaxation run. 
            }
        }
        
        var wmass -type REAL { 
            default {
                0.75*Tot_Mass/pi**2 for Parrinello-Rahman MD;
                0.75*Tot_Mass/pi**2/Omega**(2/3) for Wentzcovitch MD
            }
            info {
                Fictitious cell mass [amu] for variable-cell simulations
                (both 'vc-md' and 'vc-relax')
            }
        }

        var cell_factor -type REAL { 
            default { 2.0 for variable-cell calculations, 1.0 otherwise }
            info {
                Used in the construction of the pseudopotential tables.
                It should exceed the maximum linear contraction of the
                cell during a simulation.
            }
        }
        
        var press_conv_thr -type REAL { 
            default { 0.5D0 Kbar }
            info {
                Convergence threshold on the pressure for variable cell
                relaxation ('vc-relax' : note that the other convergence
                            thresholds for ionic relaxation apply as well).
            }
        }
        
        var cell_dofree -type CHARACTER { 
            default { 'all' }
	    options {
		info {
		    Select which of the cell parameters should be moved:
		}                
                opt -val 'all'     { all axis and angles are moved }
                opt -val 'x'       { only the x component of axis 1 (v1_x) is moved }
                opt -val 'y'       { only the y component of axis 2 (v2_y) is moved }
                opt -val 'z'       { only the z component of axis 3 (v3_z) is moved }
                opt -val 'xy'      { only v1_x and v2_y are moved }
                opt -val 'xz'      { only v1_x and v3_z are moved }
                opt -val 'yz'      { only v2_y and v3_z are moved }
                opt -val 'xyz'     { only v1_x, v2_y, v3_z are moved }
                opt -val 'shape'   { all axis and angles, keeping the volume fixed }
                opt -val 'volume'  { the volume changes, keeping all angles fixed (i.e. only celldm(1) changes) }
                opt -val '2Dxy'    { only x and y components are allowed to change }
                opt -val '2Dshape' { as above, keeping the area in xy plane fixed }
		info {
		    BEWARE: if axis are not orthogonal, some of these options do not
		            work (symmetry is broken). If you are not happy with them, 
		            edit subroutine init_dofree in file Modules/cell_base.f90
		}
            }
        }
    }



    #
    # card ATOMIC_SPECIES
    #
    card ATOMIC_SPECIES {
        syntax {
            table atomic_species {
                rows -start 1 -end ntyp {
                    col X -type CHARACTER {
                        info { 
                            label of the atom. Acceptable syntax:
                            chemical symbol X (1 or 2 characters, case-insensitive) 
                            or chemical symbol plus a number or a letter, as in
                            "Xn" (e.g. Fe1) or "X_*" or "X-*" (e.g. C1, C_h;
                            max total length cannot exceed 3 characters)
                        }
                    }
                    col Mass_X -type REAL {
                        info {
                            mass of the atomic species [amu: mass of C = 12]
                            Used only when performing Molecular Dynamics run
                            or structural optimization runs using Damped MD.
                            Not actually used in all other cases (but stored
                            in data files, so phonon calculations will use
                            these values unless other values are provided)
                        }
                    }
                    col PseudoPot_X -type CHARACTER {
                        info {
                            File containing PP for this species.
            
                            The pseudopotential file is assumed to be in the new UPF format.
                            If it doesn't work, the pseudopotential format is determined by
                            the file name:
                            
                            *.vdb or *.van     Vanderbilt US pseudopotential code
                            *.RRKJ3            Andrea Dal Corso's code (old format)
                            none of the above  old PWscf norm-conserving format
                        }
                    }
                }
            }
        }
    }

    #
    # card ATOMIC_POSITIONS
    #

    card ATOMIC_POSITIONS {

        flag atompos_unit -use optional {
            enum { alat | bohr | angstrom | crystal | crystal_sg }
            default { (DEPRECATED) alat }
            options {
                info {
                    Units for ATOMIC_POSITIONS:
                }
                opt -val alat {
                    atomic positions are in cartesian coordinates, in
                    units of the lattice parameter (either celldm(1) 
                    or A). If no option is specified, 'alat' is assumed;
                    not specifying units is DEPRECATED and will no
                    longer be allowed in the future
                }
                
                opt -val bohr {
                    atomic positions are in cartesian coordinate, 
                    in atomic units (i.e. Bohr radii)
                }
                
                opt -val angstrom {
                    atomic positions are in cartesian coordinates, in Angstrom
                }
                
                opt -val crystal {
                    atomic positions are in crystal coordinates, i.e.
                    in relative coordinates of the primitive lattice
                    vectors as defined either in card @ref CELL_PARAMETERS
                    or via the ibrav + celldm / a,b,c... variables
                }

                opt -val crystal_sg {
                    atomic positions are in crystal coordinates, i.e.
                    in relative coordinates of the primitive lattice.
                    This option differs from the previous one because
                    in this case only the symmetry inequivalent atoms
                    are given. The variable space_group must indicate
                    the space group number used to find the symmetry
                    equivalent atoms. The other variables that control 
                    this option are uniqueb, origin_choice, and 
                    rhombohedral.
                }
            }
        }

        choose {
            when -test "calculation == 'bands' OR calculation == 'nscf'" {
                message { 
                    Specified atomic positions will be IGNORED and those from the
                    previous scf calculation will be used instead !!!
                }
            }
            otherwise  {
                syntax {
                    
                    table atomic_coordinates {
                        rows -start 1 -end nat {
                            col X -type CHARACTER {
                                info { label of the atom as specified in @ref ATOMIC_SPECIES }
                            }

                            colgroup -type REAL {
                                info { 
                                    atomic positions 
                                    
                                    NOTE: each atomic coordinate can also be specified as a simple algebraic expression.
                                          To be interpreted correctly expression must NOT contain any blank
                                          space and must NOT start with a "+" sign. The available expressions are:
                                          
                                            + (plus), - (minus), / (division), * (multiplication), ^ (power)

                                          All numerical constants included are considered as double-precision numbers;
                                          i.e. 1/2 is 0.5, not zero. Other functions, such as sin, sqrt or exp are
                                          not available, although sqrt can be replaced with ^(1/2). 

                                          Example:
                                                C  1/3   1/2*3^(-1/2)   0
                                        
                                          is equivalent to

                                                C  0.333333  0.288675  0.000000 

                                          Please note that this feature is NOT supported by XCrysDen (which will
                                          display a wrong structure, or nothing at all).         

                                          When atomic positions are of type crystal_sg coordinates can be given 
                                          in the following four forms (Wyckoff positions):
                                             C  1a 
                                             C  8g   x 
                                             C  24m  x y 
                                             C  48n  x y z
                                          The first form must be used when the Wyckoff letter determines uniquely 
                                          all three coordinates, forms 2,3,4 when the Wyckoff letter and 1,2,3
                                          coordinates respectively are needed.
                                          
                                          The forms:
                                             C 8g  x  x  x
                                             C 24m x  x  y 
                                          are not allowed, but
                                             C x x x
                                             C x x y
                                             C x y z
                                          are correct.
                                }
                                col x
                                col y
                                col z
                            }
                            
                            optional {
                                colgroup -type INTEGER {                                                
                                    info {
                                        component i of the force for this atom is multiplied by if_pos(i),
                                        which must be either 0 or 1.  Used to keep selected atoms and/or
                                        selected components fixed in MD dynamics or
                                        structural optimization run.
                                           
                                        With crystal_sg atomic coordinates the constraints are copied in all equivalent
                                        atoms.
                                    }
                                    default { 1 }
                                    
                                    col if_pos(1)
                                    col if_pos(2)
                                    col if_pos(3)
                                }
                            }
                        }
                    }
                }

            }
        }
    }    


    #
    # K_POINTS
    #
    card K_POINTS {
        flag kpoint_type -use optional {
            enum { tpiba | automatic | crystal | gamma | tpiba_b | crystal_b | tpiba_c | crystal_c }
            default { tbipa }
            options {
                info {
                    K_POINTS options are:
                }
                opt -val tpiba    {
                    read k-points in cartesian coordinates, 
                    in units of 2 pi/a (default)
                }

                opt -val automatic {
                    automatically generated uniform grid of k-points, i.e,
                    generates ( nk1, nk2, nk3 ) grid with ( sk1, sk2, sk3 ) offset.
                    nk1, nk2, nk3 as in Monkhorst-Pack grids
                    k1, k2, k3 must be 0 ( no offset ) or 1 ( grid displaced
                    by half a grid step in the corresponding direction ) 
                    BEWARE: only grids having the full symmetry of the crystal
                            work with tetrahedra. Some grids with offset may not work.
                }
 
                opt -val crystal  {
                    read k-points in crystal coordinates, i.e. in relative
                    coordinates of the reciprocal lattice vectors
                }

                opt -val gamma {
                    use k = 0 (no need to list k-point specifications after card)
                    In this case wavefunctions can be chosen as real, 
                    and specialized subroutines optimized for calculations
                    at the gamma point are used (memory and cpu requirements 
                    are reduced by approximately one half).
                }

                opt -val tpiba_b {
                    Used for band-structure plots.
                    k-points are in units of  2 pi/a. 
                    nks points specify nks-1 lines in reciprocal space.
                    Every couple of points identifies the initial and
                    final point of a line. pw.x generates N intermediate
                    points of the line where N is the weight of the first point.
                }

                opt -val crystal_b {
                    As tpiba_b, but k-points are in crystal coordinates.
                }

                opt -val tpiba_c {
                    Used for band-structure contour plots. 
                    k-points are in units of  2 @i pi/a. nks must be 3.
                    3 k-points k_0, k_1, and k_2 specify a rectangle 
                    in reciprocal space of vertices k_0, k_1, k_2, 
                    k_1 + k_2 - k_0: k_0 + \alpha (k_1-k_0)+
                    \beta (k_2-k_0) with 0 <\alpha,\beta < 1. 
                    The code produces a uniform mesh n1 x n2 
                    k points in this rectangle. n1 and n2 are 
                    the weights of k_1 and k_2. The weight of k_0
                    is not used.
                }

                opt -val crystal_c {
                    As tpiba_c, but k-points are in crystal coordinates.
                }
            }
        }

        choose {
            when -test "tpiba  OR  crystal  OR  tpiba_b  OR  crystal_b OR tpiba_c OR crystal_c" {
                syntax -flag {tpiba | crystal | tpiba_b | crystal_b | tpiba_c | crystal_c } {
                    line { 
                        var nks -type INTEGER {
                            info {Number of supplied special k-points.}
                        }
                    }
                    table kpoints {
                        rows -start 1 -end nks {
                            colgroup -type REAL {
                                col xk_x 
                                col xk_y
                                col xk_z
                                col wk
                                info {
                                    Special k-points (xk_x/y/z) in the irreducible Brillouin Zone
                                    (IBZ) of the lattice (with all symmetries) and weights (wk)
                                    See the literature for lists of special points and
                                    the corresponding weights.
                                    
                                    If the symmetry is lower than the full symmetry
                                    of the lattice, additional points with appropriate
                                    weights are generated. Notice that such procedure
                                    assumes that ONLY k-points in the IBZ are provided in input

                                    In a non-scf calculation, weights do not affect the results.
                                    If you just need eigenvalues and eigenvectors (for instance,
                                    for a band-structure plot), weights can be set to any value
                                    (for instance all equal to 1).
                                }
                            }
                        }
                    }
                }               
            }
            elsewhen -test "automatic" {
                syntax -flag {automatic} {
                    line {
                        vargroup -type INTEGER {
                            var nk1
                            var nk2
                            var nk3 
                            info { 
                                These parameters specify the k-point grid 
                                (nk1 x nk2 x nk3) as in Monkhorst-Pack grids. 
                            }
                        }
                        vargroup -type INTEGER {
                            var sk1
                            var sk2
                            var sk3
                            info {
                                The grid offsets;  sk1, sk2, sk3 must be 
                                0 ( no offset ) or 1 ( grid displaced by 
                                half a grid step in the corresponding direction ).
                            }
                        }
                    }
                }
            }
            elsewhen -test "gamma" {
                syntax -flag {gamma} {}
            }
        }
    }

    #
    # CELL_PARAMETERS
    #
    card CELL_PARAMETERS {
        flag lattice_type -use optional {
            enum { alat | bohr | angstrom }
            info {
                Unit for lattice vectors; options are:
                
                @b 'bohr' / @b 'angstrom':
                                     lattice vectors in bohr-radii / angstrom.
                                     In this case the lattice parameter alat = sqrt(v1*v1).
                
                @b 'alat' / nothing specified:
                                     lattice vectors in units of the lattice parameter (either
                                     @ref celldm(1) or @ref A). Not specifying units is DEPRECATED
		                     and will not be allowed in the future.

                If neither unit nor lattice parameter are specified,
                'bohr' is assumed - DEPRECATED, will no longer be allowed
            }
        }
        
        label { 
            Optional card, needed only if @ref ibrav == 0 is specified, ignored otherwise ! 
        }
        
        syntax {
            table lattice {
                cols -start 1 -end 3 {
                    rowgroup -type REAL {
                        info { 
                            Crystal lattice vectors (in cartesian axis):
                                v1(1)  v1(2)  v1(3)    ... 1st lattice vector
                                v2(1)  v2(2)  v2(3)    ... 2nd lattice vector
                                v3(1)  v3(2)  v3(3)    ... 3rd lattice vector
                        }                   
                        row v1
                        row v2
                        row v3
                    }
                }
            }
        }
    }


    #
    # CONSTRAINTS
    #

    card CONSTRAINTS {
        label {
            Optional card, used for constrained dynamics or constrained optimisations
            (only if @ref ion_dynamics=='damp' or 'verlet', variable-cell excepted)
        }
        message {
            When this card is present the SHAKE algorithm is automatically used.
        }

        syntax {
            line {
                var nconstr -type INTEGER {
                    info { Number of constraints. }
                }
                
                optional {
                    var constr_tol -type REAL {
                        info { Tolerance for keeping the constraints satisfied. }
                    }
                }
            }
            
            table constraints_table {
                rows -start 1 -end nconstr {
                    col constr_type -type CHARACTER {
			options {
                            info {
                                Type of constraint :
                            }
                            opt -val 'type_coord' {
				constraint on global coordination-number, i.e. the
				average number of atoms of type B surrounding the
				atoms of type A. The coordination is defined by
				using a Fermi-Dirac.
				(four indexes must be specified).
			    }
                            opt -val 'atom_coord' {
				constraint on local coordination-number, i.e. the
				average number of atoms of type A surrounding a
				specific atom. The coordination is defined by
				using a Fermi-Dirac.
				(four indexes must be specified).
			    }
                            opt -val 'distance' {
				constraint on interatomic distance 
				(two atom indexes must be specified).
			    }
                            opt -val 'planar_angle' {
				constraint on planar angle 
				(three atom indexes must be specified).
			    }
                            opt -val 'torsional_angle' {
				constraint on torsional angle 
				(four atom indexes must be specified).
			    }
                            opt -val 'bennett_proj' {
				constraint on the projection onto a given direction
				of the vector defined by the position of one atom
				minus the center of mass of the others.
				G. Roma, J.P. Crocombette: J. Nucl. Mater. 403, 32 (2010),
				doi:10.1016/j.jnucmat.2010.06.001
			    }
                        }                       
                    }
                    colgroup {
                        col constr(1)
                        col constr(2)
                        conditional {
                            col constr(3)
                            col constr(4)
                        }
                        info {
                            These variables have different meanings for different constraint types:

                            @b 'type_coord' :
			                   @i constr(1) is the first index of the atomic type involved
                                           @i constr(2) is the second index of the atomic type involved
                                           @i constr(3) is the cut-off radius for estimating the coordination
                                           @i constr(4) is a smoothing parameter

                            @b 'atom_coord' :
			                   @i constr(1) is the atom index of the atom with constrained coordination
                                           @i constr(2) is the index of the atomic type involved in the coordination
                                           @i constr(3) is the cut-off radius for estimating the coordination
                                           @i constr(4) is a smoothing parameter

                            @b 'distance' :
			                   atoms indices object of the constraint, as they appear in
                                           the @ref ATOMIC_POSITIONS card

                            @b 'planar_angle', @b 'torsional_angle' :
			                   atoms indices object of the constraint, as they appear in the
			                   @ref ATOMIC_POSITIONS card (beware the order)

                            @b 'bennett_proj' :
			                   @i constr(1) is the index of the atom whose position is constrained.
                                           @i constr(2:4) are the three coordinates of the vector that specifies
                                           the constraint direction.
                        }
                    }

                    optional {
                        col constr_target -type REAL {
                            info {
                                Target for the constrain ( angles are specified in degrees ).
                                This variable is optional.
                            }
                        }
                    }
                }
            }
        }
    }

    #
    # card OCCUPATIONS
    #
    card OCCUPATIONS {
        label { Optional card, used only if @ref occupations == 'from_input', ignored otherwise ! }
        syntax {
            table occupations_table {
                cols -start 1 -end nbnd {
                    row f_inp1 -type REAL {
                        info { 
                            Occupations of individual states (MAX 10 PER ROW). 
                            For spin-polarized calculations, these are majority spin states. 
                        }
                    }
                    conditional {
                        row f_inp2 -type REAL {
                            info {                              
                                Occupations of minority spin states (MAX 10 PER ROW)
                                To be specified only for spin-polarized calculations.
                            }
                        }
                    }
                }
            }
        }
    }    

    #
    # card ATOMIC_FORCES
    #

    card ATOMIC_FORCES { 
        label { Optional card used to specify external forces acting on atoms. }
        message {
            BEWARE: if the sum of external forces is not zero, the center of mass of
                    the system will move
        }
        syntax {
            table atomic_forces {
               rows -start 1 -end nat {
                  col X -type CHARACTER {
                     info { label of the atom as specified in @ref ATOMIC_SPECIES }
                 }
                  colgroup -type REAL {
                      info { external force on atom X (cartesian components, Ry/a.u. units)
                     }
                      col fx
                      col fy
                     col fz
                  }
              }
           }
        }
    }   
}