!
! Spectra correction tool by Oana Bunau and Matteo Calandra, Agust 2015
!
!   This small code allows to
!
!      1) Remove states below a certain energy from the spectrum
!           In large gap insulator it should work as the usual
!           cut_occupied_states option but it is much much faster
!           In metals/semimetals the normal and more time consuming
!           option cut_occupied_states=.true. used in XSpectra 
!           should work better. The procedure use here can sometimes
!           work for metals but care is needed.
!
!      2) For L23 edges, this code generates the full L23 spectrum from
!           the L2 edge only. the L3 edge is obtained multiplying by two the
!           L2 and shifting it by the spin-orbit splitting between 2p1/2
!           and 2p3/2. Thus the spectrum in input must be the L2 edge.
!
!      3) Convolute a given spectrum known on a regular energy grid with
!         a constant lorentz brodening gamma_hole, or with an atan 
!         broadening. In more details (s_in, s_out are cross sections):
!
!        s_out(W)=integral s_in(om)*Gamma(W)/(Gamma(W)**2+(om-W)**2)/pi
!
!        and the integral is over all the space (-infty, infty). 
!
!        If conv_type='lorentz' then Gamma(W)=gamma_hole constant
!
!        If conv_type='lorentz_atan' then 
!              Gamma(W)=gamma_hole   for W < xe0
!                      =Gamma_MAX*(0.5+atan(e-1/(e*e))) otherwise
!          where e=(W-xe0)/(Ectr-xe0)
!          and Ectr is the inflection point of the atan and xe0 is
!          the pre-edge onset.
!          For the definition of e see Eq. 7 and below in 
!           O. Bunau and M. Calandra, PRB 87, 205105 (2013) 
!       
!          Finally emin_conv, emax_conv and nenergy_conv define
!          the energy grid of the convoluted spectrum (energies labeled W above).
!          If omitted, the energy grid is the same as in the input cross section.
!
!          Important, please note that the convolution adds on TOP of the
!          width of your original spectrum. So you should run xspectra with a 
!          tiny xgamma.
!------------------------------------------------------------------------------------
!  How to use:
!      
!      1) Use in single processor, no parallelization
!
!      2) Input file description:
!
!              case (i): removal of occupied states from the spectrum
!
!                     &input_manip 
!                       cross_section_file='xanes.dat', 
!                       option='cut_occ_states',
!                       xe0=13.0, 
!                       shift_spectrum=.false.,
!                     &end
!
!                     if shift_spectrum=.true. the spectrum is shifted in xe0
!
!              case (ii): removal of occupied states from the spectrum
!
!                     &input_manip
!                       cross_section_file='xanes.dat',
!                       option='add_L2_L3',
!                       element='Cu',
!                     &end
!
!                     element is used to read the spin orbit splitting 2p1/2, 2p3/2
!
!              The cross_section_file is the xanes.dat file with the cross section.
!
!              case (iii) - lorentz
!
!                       &input_manip 
!                         cross_section_file='xanes.dat.L23', 
!                         option='convolution',
!                         shift_spectrum=.false.,
!                         element='Cu',
!                         conv_type='lorentz',
!                         gamma_hole=1.0, 
!                         emin_conv=-50.0,
!                         emax_conv=100.0,
!                         nenergy_conv=1000,
!                       &end
!                        
!                       emin_conv, emax_conv and nenergy_conv can be omitted
!
!
!              case (iii) - lorentz_atan
!
!                    &input_manip 
!                       cross_section_file='xanes.dat.L23', 
!                       option='convolution',
!                       shift_spectrum=.false.,
!                       element='Cu',
!                       conv_type='lorentz_atan',
!                       gamma_hole=0.05, 
!                       gamma_max=6.0, 
!                       ectr=-8.0,
!                       xe0=-19.0,
!                    &end
!
!
!                 
!----------------------------------------------------------------------------