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

The past few years has brought renewed focus on the physics behind the class of materials characterized by long-range interactions and wide regions of low electron density, sparse matter. There is now much work on developing the appropriate algorithms and codes able to correctly describe this class of materials within a parameter-free quantum physical description. In particular, van der Waals (vdW) forces play a major role in building up material cohesion in sparse matter. This work presents an application to the vanadium pentoxide (V2O5) bulk structure of two versions of the vdW-DF method, a first-principles procedure for the inclusion of vdW interactions in the context of density functional theory (DFT). In addition to showing improvement compared to traditional semilocal calculations of DFT, we discuss the choice of various exchange functionals and point out issues that may arise when treating systems with large amounts of vacuum.Comment: 5 pages, 4 figures, 1 tabl

van der Waals density functional calculations of binding in molecular crystals

A recent paper [J. Chem. Phys. 132, 134705 (2010)] illustrated the potential of the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004)] for efficient first-principle accounts of structure and cohesion in molecular crystals. Since then, modifications of the original vdW-DF version (identified as vdW-DF1) has been proposed, and there is also a new version called vdW-DF2 [ArXiv 1003.5255], within the vdW-DF framework. Here we investigate the performance and nature of the modifications and the new version for the binding of a set of simple molecular crystals: hexamine, dodecahedrane, C60, and graphite. These extended systems provide benchmarks for computational methods dealing with sparse matter. We show that a previously documented enhancement of non-local correlations of vdW-DF1 over an asymptotic atom-based account close to and a few A, beyond binding separation persists in vdW-DF2. The calculation and analysis of the binding in molecular crystals requires appropriate computational tools. In this paper, we also present details on our real-space parallel implementation of the vdW-DF correlation and on the method used to generate asymptotic atom-based pair potentials based on vdW-DF.Comment: 5 pages, 4 figure

Desorption of n-alkanes from graphene: a van der Waals density functional study

A recent study of temperature programmed desorption (TPD) measurements of small n-alkanes (CNH2N+2) from C(0001) deposited on Pt(111) shows a linear relationship of the desorption energy with increasing n-alkane chain length. We here present a van der Waals density functional study of the desorption barrier energy of the ten smallest n-alkanes (N = 1 to 10) from graphene. We find linear scaling with N, including a nonzero intercept with the energy axis, i.e., an offset at the extrapolation to N = 0. This calculated offset is quantitatively similar to the results of the TPD measurements. From further calculations of the polyethylene polymer we offer a suggestion for the origin of the offset.Comment: 3 pictures, 1 tabl

Application of van der Waals Density Functional to an Extended System: Adsorption of Benzene and Naphthalene on Graphite

It is shown that it is now possible to include van der Waals interactions via a nonempirical implementation of density functional theory to describe the correlation energy in electronic structure calculations on infinite systems of no particular symmetry. The vdW-DF functional [Phys. Rev. Lett. 92, 246401 (2004)] is applied to the adsorption of benzene and naphthalene on an infinite sheet of graphite, as well as the binding between two graphite sheets. Comparison with recent thermal desorption data [Phys. Rev. B 69, 535406 (2004)] shows great promise for the vdW-DF method.Comment: 4 pages, 3 figure