Interpretation of the Hartree-Fock interaction energy between closed-shell systems

Abstract

In the present paper a decomposition of the Hartree-Fock interaction energy of two closed-shell systems is given. The decomposition is obtained by performing the Hartree-Fock iterations for the supersystem in a way different from the traditional one. The procedure is called the Pauli blockade method since the interacting molecules are deformed in the field of their partners under the constraint that they cannot penetrate each others occupied spaces. The zeroth iteration of the above procedure gives the Heitler-London interaction energy and in the consecutive iterations the total energy of the supersystem is minimized letting the charge distribution of molecule A adapt itself to the presence of molecule B and vice versa, until self-consistency is achieved. It is also shown that unphysical charge transfer may occur in some methods if during mutual deformations the intersystem Pauli exclusion principle is not observed. This confirms earlier suggestions that the so called weak symmetry forcing in the perturbation approach to intermolecular interactions is insufficient and may lead to results which are qualitatively incorrect.