New Scaled Atoms-in-Molecules Theory for Predicting Diatomic Potential-Energy Curves. I. General Theory and Application to H2 and He2+ +

Abstract

An exact scaled atoms‐in‐molecules theory for predicting potential‐energy curves and other properties of diatomic molecules is developed. The basis consists, in the first place, of linear combinations of antisymmetrized products of atomic substate eigenfunctions. Each such basis function ψ_n can be modified by introducing variational scaling parameters s_n^A and s_n^B into its component atomic eigenfunctions. Exact equations are developed for determining, by reference to experimental atomic properties, all intra‐atomic contributions to the energy matrix elements. All remaining parts of the energy matrix elements are interatomic in nature, and these parts are computed using previously determined approximate atomic eigenfunctions; as the latter are successively made more accurate, results of the diatomic calculation should converge to experiment. A restricted orbital model, which reduces the number of independent nonlinear variational parameters, is also proposed. Initial applications to ground and excited electronic state of H₂ and He₂^{+ +} are presented. A potentially useful approximate calibration technique is suggested and tested.