Local and non-local dispersion models

Abstract

When two molecules approach closely, the polarisation of each by the other must often be described by non-local distributed polarizabilities, and this implies that the dispersion interaction must also have a non-local form. Conventional models, however, successfully use a local atom-atom dispersion interaction. We describe ways in which these two versions of the dispersion interaction may be reconciled. Many of the non-local terms are small, and can be neglected; others cancel to some extent. For diatomics it is possible to transform the non-local expression accurately into a local site-site form, at the cost of introducing a third site. For larger molecules a similar procedure may be used, but it may not be possible to remove the non-local behaviour entirely. © 1989.