A Qbox Implementation of van der Waals Density Functionals with Applications*

We present an implementation of the non-local van der Waals correlation functional proposed by Dion et al. [1] in the Qbox code [2]. We develop a simple approach to remove the logarithmic singularity in the kernel function, and derive the non-local potential needed for self-consistent calculations of energies, ionic forces and stress for simulations in arbitrary-shaped unit cells. We compare the performance of five different van der Waals functionals in applications to the benzene-water dimer, the benzene crystal and other organic molecular crystals. \\[4pt] [1] M. Dion et al. Phys. Rev. Lett. 92, 246401 (2004)\\[0pt] [2] http://eslab.ucdavis.edu/software/qbox