Linear response theory of molecular interaction: Correlated Π electron systems

Abstract

A many-body theory of molecular interaction is presented for systems of nonoverlapping molecules containing delocalized Π electrons. The theory is based on a combination of LCAO MO theory and time-dependent Hartree linear response theory. A multipole expansion of the Coulomb interaction is not employed rendering the theory applicable to large molecules. Some aspects of electron correlation are included. The infinite order result for the dispersion interaction is the change in the intermolecular correlation energy associated with ’’turning on’’ the Coulomb potential. A closed-form infinite order expression for the intermolecular permanent moment interaction accounts for the modification of the bare Coulomb interaction by the polarizable system. Second order results that include all orders of intramolecular correlation for the dispersion and static interactions are also obtained. These are expanded in terms of the intramolecular correlation. A three-body dispersion potential that includes all orders of intramolecular correlation is also presented. The theory is amenable to numerical analysis and provides a method to investigate the convergence of various perturbation series.