Van der Waals Density Functional for Layered Structures

TL;DR

This paper applies a fully nonlocal van der Waals density functional within DFT to layered materials, successfully capturing weak interlayer forces that traditional GGA functionals fail to describe accurately.

Contribution

It demonstrates that a fully nonlocal van der Waals functional improves DFT calculations for layered structures over standard GGA methods.

Findings

Accurate bond lengths and binding energies for graphite, boron nitride, and molybdenum sulfide

DFT with GGA fails for sparse matter properties

Nonlocal functional captures weak interlayer interactions

Abstract

To understand sparse systems we must account for both strong local atom bonds and weak nonlocal van der Waals forces between atoms separated by empty space. A fully nonlocal functional form [H. Rydberg, B.I. Lundqvist, D.C. Langreth, and M. Dion, Phys. Rev. B 62, 6997 (2000)] of density-functional theory (DFT) is applied here to the layered systems graphite, boron nitride, and molybdenum sulfide to compute bond lengths, binding energies, and compressibilities. These key examples show that the DFT with the generalized-gradient approximation does not apply for calculating properties of sparse matter, while use of the fully nonlocal version appears to be one way to proceed.