Formulations of the closed-shell interactions in endohedral systems.

An attempt is made to express the interaction energy in an endohedral A@B system starting from a one-center (r(<))(l)/(r(>))(l+1) expansion. Electrostatic, induction, and dispersion contributions are obtained from Rayleigh-Schrödinger perturbation theory. New electric polarizabilities with r(-l-1) radial integrals are calculated for l = 0, 1 and 2 for the outer system B. For a 'breakable'B, they can be related to the usual London formula. The new polarizabilities are used to successfully estimate the Born-type charge solvation energy and to roughly estimate the lowest-order, l = 1 dispersion term. The latter, London-type expression is now also derived from a Casimir-Polder-type argument. It is applied on A = He-Xe, Zn-Hg, and several molecules with B = C(60) and the results are compared against MP2 and SCS-MP2 supramolecular calculations. The l = 2 dispersion terms are smaller than the l = 1 ones.