van der Waals bonded materials: vanadium pentoxide bulk structure

In this work we present a computational study of the layered oxide structure of vanadium pentoxide (V$_2$O$_5$) using the vdW-DF functional (M. Dion et al., Phys.Rev.Lett. \textbf{92}, 246401 (2004); T. Thonhauser et al., Phys. Rev. B \textbf{76}, 125112 (2007); K. Lee et al., Phys. Rev. B \textbf{82}, 081101 (2010)) which has proven to be able to capture the essential van der Waals interactions across matter separated by charge voids. We show that these forces play a substantial role for the description of the lattice constants and cohesion of this compound. In addition we document and handle a sensitivity to numerical noise in the evaluation of some exchange versions used with nonlocal correlation.