Quantum Mechanics of the H2–H2 Interaction. V. The Importance of Intermolecular Charge-Transfer States

Abstract

In a preceding paper a one‐configuration wavefunction of strong orthogonal group functions was found to give a rather poor description of the orientation dependence of short‐range intermolecular forces in H₂–H₂. As an alternative to the necessity of relaxing the strong orthogonality condition, it is suggested that the introduction of a small amount of the charge‐transfer state H₂⁻–H₂⁺ describing one‐electron transfer between the two molecules should improve the interaction energy and its change with the relative molecular orientation. Ab initio calculations in a region of intermolecular separations ranging from two to four times the internuclear equilibrium distance of an isolated H₂ molecule show that less than 1% of such a charge‐transfer state gives interaction energies which are in substantial agreement with those obtained with a complete configurational interaction.