Ab initio calculations of exchange repulsion between two Ar atoms

Abstract

The first order exchange energy for the Ar-Ar interaction has been calculated using an SCF wavefunction for Ar in a large gaussian basis set. It is shown that in the region of the van der Waals minimum more than 95 per cent of the first order exchange originates from the interaction of M-shell electrons and that three-orbital terms dominate this interaction. The terms of the order S ⁴ prove to be negligible. Interaction energies from SCF supermolecule calculations are also given.