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 Cab, 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.
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