  Sparse matter is characterized by regions with low electron density and its
understanding calls for methods to accurately calculate both the van der Waals
(vdW) interactions and other bonding. Here we present a first-principles
density functional theory (DFT) study of a layered oxide (V2O5) bulk structure
which shows charge voids in between the layers and we highlight the role of the
vdW forces in building up material cohesion. The result of previous
first-principles studies involving semilocal approximations to the
exchange-correlation functional in DFT gave results in good agreement with
experiments for the two in-plane lattice parameters of the unit cell but
overestimated the parameter for the stacking direction. To recover the third
parameter we include the nonlocal (dispersive) vdW interactions through the
vdW-DF method [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] testing also
various choices of exchange flavors. We find that the transferable
first-principle vdW-DF calculations stabilizes the bulk structure. The vdW-DF
method gives results in fairly good agreement with experiments for all three
lattice parameters.
