Range and strength of interatomic forces: dispersion and induction contributions to the bonds of dications and of ionic molecules Original Research Article

An application of previously introduced correlation formulas in terms of polarizabilities of interacting species permits an assessment of the relative role of dispersion and induction contributions to describe bond lengths and energies in some doubly charged ion-neutral systems (the dications of alkaline earth atoms and rare gases). An extension to ion-ion systems is also presented, on the basis of an empirical analysis of available data on alkali halides, in order to establish the role of both dispersion and induction interactions as compared to Coulomb attraction. An improved version of the Slater-Kirkwood formulation with an appropriate choice for the effective electron numbers is suggested to estimate the long range effective dispersion coefficients. The present approach provides a unifying framework for the characterization of bonds for systems which greatly vary in size and strength and recipes are suggested for interatomic potential energy curves. It is concluded that this approach is also relevant as a starting point for extensions to include anisotropies due both to orbital overlap for open shell partners and to mutual orientation when molecules are considered.