On the exchange polarization effects in the interaction of two helium atoms

Abstract

The induction and the dispersion components of the exchange polarization energy are calculated for the interaction of two ground-state helium atoms. The calculations are made within the framework of a double perturbation theory with the neglect of all intra-atomic correlation effects. Two zeroth-order operators, the Hartree and the Hartree-Fock are considered, the former yielding much better results than the latter. At the van der Waals minimum the exchange polarization energy is positive and decreases the interaction energy by about 7 per cent. The calculated value of a well depth amounts to 13·4 K, which should be considered as an upper limit because of the neglect of intra-atomic correlation. When approximately corrected for the latter a lower limit of 10·7 K is obtained. It is also shown that over 90 per cent of the exchange dispersion energy can be obtained by using a simplified formula involving only one two-electron integral over a relevant pair function.