libvdwxc is a library which provides fast and scalable implementations of non-local van der Waals density functionals in the vdW-DF family. To use libvdwxc, you need to install it and compile GPAW with it. libvdwxc can be used with other semilocal functionals like optPBE, optB88, and BEEF-vdW.

Install libvdwxc, making sure that its dependencies FFTW3 and FFTW3-MPI are available on the system. For truly large systems, you may install PFFT to achieve better scalability. For realistically-sized systems, FFTW3-MPI is efficient and might be a bit faster than PFFT.

Run a calculation by specifying backend, like {‘name’:’BEEF-vdW’, ‘backend’:’libvdwxc’}, as in this example:

from import molecule
from gpaw import GPAW

atoms = molecule('H2O')
# There are these functionals: vdW-DF, vdW-DF2, vdW-DF-cx, optPBE-vdW,
# optB88-vdW, C09-vdW, BEEF-vdW, and mBEEF-vdW.
# There are three modes: serial, mpi, and pfft. Default is auto.
calc = GPAW(mode='fd',
            xc={'name': 'BEEF-vdW', 'backend': 'libvdwxc', 'mode': 'mpi'})
atoms.calc = calc

libvdwxc will automatically parallelize with as many cores as are available for domain decomposition. If you parallelize over k-points or bands, and especially if you use planewave mode, be sure to pass the parallelization keyword augment_grids=True to make use of all cores including those for k-point and band parallelization (see Parallel runs).

Note that libvdwxc 0.4 has no stress term implementation.