2.4 Libraries

QUANTUM ESPRESSO makes use of the following external libraries:

• BLAS (http://www.netlib.org/blas/) and
• LAPACK (http://www.netlib.org/lapack/) for linear algebra
• FFTW (http://www.fftw.org/) for Fast Fourier Transforms

A copy of the needed routines is provided with the distribution. However, when available, optimized vendor-specific libraries should be used: this often yields huge performance gains.

2.4.0.1 BLAS and LAPACK

QUANTUM ESPRESSO can use any architecture-optimized BLAS and LAPACK replacements, like those contained e.g. in the following libraries:

MKL for Intel CPUs
ACML for AMD CPUs
ESSL for IBM machines
SCSL for SGI Altix
SUNperf for Sun

If none of these is available, we suggest that you use the optimized ATLAS library: see
http://math-atlas.sourceforge.net/. Note that ATLAS is not a complete replacement for LAPACK: it contains all of the BLAS, plus the LU code, plus the full storage Cholesky code. Follow the instructions in the ATLAS distributions to produce a full LAPACK replacement.

Sergei Lisenkov reported success and good performances with optimized BLAS by Kazushige Goto. The library is now available under an open-source license: see the GotoBLAS2 page at
http://www.tacc.utexas.edu/tacc-software/gotoblas2/.

2.4.0.2 FFT

QUANTUM ESPRESSO has an internal copy of an old FFTW library. It also supports the newer FFTW3 library and some vendor-specific FFT libraries. configure will first search for vendor-specific FFT libraries; if none is found, it will search for an external FFTW v.3 library; if none is found, it will fall back to the internal copy of FFTW. configure will add the appropriate preprocessing options:

• -D__LINUX_ESSL for ESSL on IBM Linux machines,
• -DASL for NEC ASL library on NEC machines,
• -D__ARM_LIB for ARM Performance library,
• -D__DFTI for DFTI (Intel MKL library),
• -D__FFTW3 for FFTW3 (external),
• -D__FFTW) for FFTW (internal library),

to DFLAGS in the make.inc file. If you edit make.inc manually, please note that one and only one among the mentioned preprocessing option must be set.

If you have MKL libraries, you may either use the provided FFTW3 interface (v.10 and later), or directly link FFTW3 from MKL (v.12 and later) or use DFTI (recent versions).

2.4.0.3 MPI libraries

MPI libraries are usually needed for parallel execution, unless you are happy with OpenMP-only multicore parallelization. In well-configured machines, configure should find the appropriate parallel compiler for you, and this should find the appropriate libraries. Since often this doesn't happen, especially on PC clusters, see Sec.2.7.7.

Note: since v.6.1, MPI libraries implementing v.3 of the standard (notably, non-blocking broadcast and gather operations) are required.

2.4.0.4 Other libraries

QUANTUM ESPRESSO can use the MASS vector math library from IBM, if available (only on AIX).

2.4.0.5 If optimized libraries are not found

The configure script attempts to find optimized libraries, but may fail if they have been installed in non-standard places. You should examine the final value of BLAS_LIBS, LAPACK_LIBS, FFT_LIBS, MPI_LIBS (if needed), MASS_LIBS (IBM only), either in the output of configure or in the generated make.inc, to check whether it found all the libraries that you intend to use.

If some library was not found, you can specify a list of directories to search in the environment variable LIBDIRS, and rerun configure; directories in the list must be separated by spaces. For example:

   ./configure LIBDIRS="/opt/intel/mkl70/lib/32 /usr/lib/math"

If this still fails, you may set some or all of the *_LIBS variables manually and retry. For example:

   ./configure BLAS_LIBS="-L/usr/lib/math -lf77blas -latlas_sse"

Beware that in this case, configure will blindly accept the specified value, and won't do any extra search.