Unified theory for the intermolecular forces between closed shell atoms and ions

A simple theoretical model for intermolecular forces is developed in such a way that it includes simultaneously the effects of short-range and long-range interactions. At long distances the calculated intermolecular forces reduce to the usual dispersion and induction effects. At short distances, the results approach those of the short-range interaction, which in the present calculation followed our previous work [J. Chem. Phys. 56, 3122 (1972)]. The results of the method are in good agreement with available experimental results for closed shell atom-atom and ion-atom interactions, over the whole range of internuclear distances.