Multistructure Valence-Bond and Atoms-in-Molecules Calculations for LiF, F2, and F2−

Abstract

Multistructure valence‐bond calculations with nonorthogonal atomic orbitals have been performed for LiF, F₂, and F₂⁻. The basis set consisted of approximate Hartree–Fock functions for the neutral atoms constructed from linear combinations of Gaussian‐type orbitals. Several empirical approaches for estimating an intra‐atomic correction are examined, and a new method is found which yields reasonable results. The new scheme, which is a modification of Moffit's “atoms‐in‐molecules” method, is thought to be somewhat preferable to the previously proposed ICC scheme of Hurley, as it gives more reasonable results in the limits of both small and large internuclear distances. The attributes of the various methods are discussed and illustrated by means of a simple H₂ calculation, as well as by application to LiF, F₂, and F₂⁻. A dissociation energy for F₂⁻ slightly larger than that for F₂ is obtained; this surprising result, which clearly requires further investigation, is briefly discussed.