Valence body study of the potential energy surface for the system He … HF

Abstract

The potential energy surface of He. HF is studied by an ab initio mixed MO-VB method. Each fragment is treated at the SCF level and the interaction energy is computed in the framework of VB theory; the sets of MOs of each fragment are left non-orthogonal even when they are made to approach one another. The method does not include any basis set superposition error. Five cuts of the surface are computed at R HF fixed at the equilibrium value of 1·7325 a.u. There is agreement with the general results of Hutson and Howard [1, 2] who derived the corresponding potentials for Ar, Kr, Xe interacting with HF and for Ne, Ar, Kr, Xe interacting with HCl from experimental data: the absolute minimum is found for the linear geometry at the He. HF approach and the secondary minimum also in the linear geometry but in the He. FH arrangement. A study of the convergence of each component of the interaction (Coulomb, exchange, induction, dispersion) is performed either by extending the basis set or increasing the number of VB structures included. It is found that the interaction can be explained in terms of Coulomb, exchange, induction and dispersion forces only; charge transfer and formation of a covalent bond are estimated to make a negligible contribution.