The vdW-DF Family of Non-Local Exchange-Correlation Functionals

Book chapter, 2017

van der Waals interactions are a phenomenon where charge fluctuations in one part of a system correlate with fluctuations in another, resulting in an attractive force. Such interactions are thus a truly non-local correlation effect. While the full—albeit unknown—density functional does include these interactions, standard local and semi-local density functionals cannot account for these non-local effects by construction and yield qualitatively erroneous predictions. The simplest expression of a non-local functional of the density rho(r) takes the form Integral[d3r d3r' rho(r) phi(r,r') rho(r')], but it was not until the end of the last century that the means to find a physically motivated, general, and transferable kernel rho emerged. The present chapter discusses the work on this kernel rho leading to the development of the successful van der Waals density functional (vdW-DF) and its variants.