Delta-function model for short-range interatomic forces: Correlation scheme for closed-shell atoms and ions

A correlation scheme is developed for the short−range interaction energies between rare−gas atoms and positive and negative ions with rare−gas configurations. The exponential form of the correlation and the relation between the exponental and pre−exponential constants are predicted by a delta−function model. The exponential constants are found to correlate with the softness parameters obtained from Hartree−Fock−Slater calculations on single atoms and ions. Comparisons are made with experimental beam scattering data, ab initio quantum−mechanical calculations, and the electron−gas model of Gordon and Kim. The over−all agreement is good.