VAN-DER-WAALS ENERGIES IN DENSITY-FUNCTIONAL THEORY

In principle, density functional theory yields the correct ground-stat e densities and energies of electronic systems under the action of a s tatic external potential. However, traditional approximations fail to include van der Waals energies between separated systems. This paper p roposes a practical procedure for remedying this difficulty. Our metho d allows seamless calculations between small and large intersystem dis tances. The asymptotic H-He and He-He interactions are calculated as a first illustration, with very accurate results.