On the role of higher-order correlation effects on the induction interactions between closed-shell molecules

Abstract

High-order correlation contributions to the second-order induction energy were studied for various representative van der Waals complexes. It was found that the induction energy obtained by the truncation of the relaxed Møller–Plesset expansion in the second or third order is in most cases quite close to the induction energy computed with the coupled-cluster method (restricted to single and double excitations). Also, the effect of triples excitations on this perturbation term is usually small. However, given an oscillatory behaviour of the Møller–Plesset induction corrections, the coupled-cluster method seems to be better suited to a reliable calculation of the induction energy. The sources of the remaining differences between the interaction energies computed by symmetry-adapted perturbation theory and those computed by the supermolecule coupled-cluster method (restricted to single, double, and noniterative triple excitations) are examined. It has been found that they can be attributed to the higher-order correlation terms in the second-order dispersion and exchange–induction corrections.