Density functional theory including Van Der Waals forces

Abstract A progress report is given of an extension of the density functional formalism to include long‐range interactions such as van der Waals or dispersion forces. This is done by proving a general expression for the so‐called exchange‐correlation energy to contain and to describe such interactions just as well as any other treatment. The proper long‐range forms of the interactions are derived explicitly in the cases of two neutral atoms, an atom outside a metal surface, and two parallel metal surfaces. The long‐standing problem of treating the attractive and repulsive forces on the same footing in this way gets a solution. For practical calculations, an approximate form, based on an analysis in the weakly inhomogeneous limit and on a limiting form of the three‐point function given by Rapcewicz and Ashcroft, is proposed and applied to some prototype cases. © 1995 John Wiley & Sons, Inc.