Definition of eigenproblems suited to intermolecular perturbation theory

Abstract

We compare the properties of those published intermolecular perturbation theories whose behavior to infinite order is understood. From both fundamental and practical viewpoints we conclude that none is completely satisfactory. Since our current, detailed understanding of these theories is derived from the eigenproblems upon which they are based, we argue that it is critical that any new perturbation theory be formulated as an eigenproblem. Since the eigenproblem upon which both the Amos–Musher (AM) and Polymeropoulos–Adams perturbation theories are based may be derived by the localized wave (LW) function method, and since both of these perturbation theories can give the ground-state energy exactly when carried to infinite order, we propose that the LW method is suitable for formulating eigenproblems upon which new perturbation theories may be based. We illustrate how the LW method may be used by deriving a new intermolecular perturbation theory, designed to be more accurate than the AM theory at large separations. Calculations on LiH show that this is the case, but that the theory becomes unsatisfactory at small separations. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 393–404, 1999