Vanadium pentoxide (V2O5): A van der Waals density functional study

Density Functional Theory (DFT) is one of the most reliable and widespread methods for the study of structure and electronic properties of materials through computers. The theory is exact in principle but for practical purposes an approximation for the exchange-correlation energy a small but crucial part of the total energy must be used. The most widely used approximations go under the name of Generalized Gradient Approximations (GGAs) and have proven to give good results for materials characterized by covalent bonds. Nevertheless they are not able to describe the van der Waals (vdW) interactions. This shortcoming leaves a proper description of a wide class of materials (sparse matter based ones) out of reach for conventional DFT calculations. The recently developed [1] functional vdW-DF with vdW interactions explicitly included, has shown to work well, yielding results for binding energies and distances in fairly good agreement with experiments. Among the systems studied are both extended (like the interlayer binding of graphite) and finite systems (such as dimers of cytosine and other DNA and RNA base-pair molecules) [2]. Here we present a van der Waals density functional calculation of the vanadium pentoxide (V2O5) bulk structure following a short overview of the nature of vdW-DF. In the V2O5 structure, each vanadium atom is connected to five oxygen atoms to create pyramids which share their corners in building a double chain. The chains are then connected along the edges to form layers stacked along the c direction. Calculations of this layered compound performed in 2004 [3] show that traditional DFT calculations fail in describing the lattice parameter in the stacking direction of the layers. When we apply the vdW-DF procedure, the bulk structure is stabilized and a result in good agreement with experiments is found.