van der Waals Density Functionals

Doktorsavhandling, 1996

Methods using local or semi local approximations (LDA, GGA etc.) for the exchange-correlation energy in the density-functional theory (DFT) do not include van der Waals interactions. To restore van der Waals interactions in DFT methods, we present van der Waals density functionals based on the response of an electron gas and on making a local-density approximation for the response to the local electromagnetic field. The functionals are applied to the asymptotic interactions in some simple model systems; two interacting atoms or molecules, an atom at a surface, and two parallel surfaces. Calculated van der Waals interaction coefficients for such systems compare favorably to results from first-principle studies. This is very encouraging and shows a way towards a general and simple way treat van der Waals interactions in density-functional theory. An important advantage of our functional is that it is easy to evaluate, which opens up possibilities for treating large systems.