Electron pair interactions in H2O, H2S, NH3, and CH4

Abstract

A simple method is presented for determining the force between two pairs of electrons that arises from the Pauli principle’s requirement that doubly occupied orbitals be orthogonal. The method does not involve wave functions that violate the Pauli principle. Strengths of the Coulomb and exchange energy interactions between electron pairs as well as the effects of the orthogonality constraints are determine in H2O, H2S, NH3, and CH4, and a comparison is made with results of a different approach for H2O and H2S. For all but one example, bond–bond repulsions are found to exert a greater effect on the internuclear angle than bond–lone pair or lone pair–lone pair forces.