Dispersion energies in systems of two closed shell atoms and/or ions

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Abstract
A semiempirical device for the calculation of the coefficients in the dispersion energy expansion for interaction between two closed shell atoms or ions is described. Summation is over all electrons. Averages of powers of electron radial coordinates are calculated with Slater-type functions. Effective quantum numbers and screening constants were determined so as to reproduce a set of like-atom rare gas dipole–dipole coefficients. These are used to extend the calculations to coefficients for unlike rare gas and ion–ion interactions, to higher multipole coefficients for those interactions, and to polarizabilities and diamagnetic susceptibilities. The effective one level energies, numbers of polarizable electrons, and accuracy of combination rules, all as determined by these calculations, are examined. Since the principal interest here is extension to ionic crystals, discussion of a questionable lattice sum for dipole–dipole interactions is appended.