Abstract
An attractive approach to intermolecular forces is to build the total wave-function for a weakly bound molecular complex from those of the unperturbed interacting fragments. A modern valence bond strategy is described which treats properly the overlap between the fragments whilst avoiding basis set superposition error. Various aspects of the approach are illustrated with recent results for the highly anisotropic atom–diatom potential of the LiH … He system.
Analogous methodology has been employed to calculate two-body interionic potentials. Preliminary results are presented for binary oxides, chlorides and fluor-ides of alkali- and alkaline-earth metals. Factors discussed include the stabilization of anions in a suitable Madelung potential, electron correlation in the fragments, and compression effects due to nearest neighbours.