ABSTRACT

The asymptotic behaviour of the dispersion interaction between molecules is shown by perturbation theory to depend in long range on inverse powers n of the intermolecular distance R and angle-dependent coefficients Cn. After a separation of the angular part of the interaction using the irreducible properties of spherical tensor operators, the dispersion constants C_ab, the basic quantum mechanical ingredient entering the calculation of dispersion coefficients, are obtained directly in terms of a generalization of the London formula involving pseudospectral decomposition of the static polarizabilities of the interacting molecules. A survey of some recent results from our Laboratory, concerning convergence of dipole polarizabilities and C₆ dispersion coefficients for one- and two-electron model systems (H, H₂⁺, He, H₂) is presented and discussed in some detail.