SUPERMOLECULAR APPROACH TO MANY-BODY DISPERSION INTERACTIONS IN WEAK VAN-DER-WAALS COMPLEXES - HE, NE, AND AR TRIMERS

Using the diagrammatic many-body perturbation theory, various three-bo dy dispersion terms that appear in the intermolecular Moller-Plesset p erturbation theory (MPPT) are identified and classified with regard to the effects of intramonomer electron correlation on the dispersion te rm. Via the connection with the supermolecular MPPT, it is demonstrate d how the leading dispersion nonadditivities arise within supermolecul ar calculations that employ MPPT or coupled cluster formalisms. The nu merical calculations for He-3, Ne-3, and Ar-3 in triangular geometries fully confirm theoretical predictions. The calculated values of dispe rsion nonadditivity clearly show that the coupled cluster theory with single, double, and noniterative triple excitations provides the prope r framework for the efficient inclusion of the intramonomer correlatio n effects in dispersion nonadditivity. The convergence of the two-body and three-body terms is shown to be very similar if we compare the th ree-body terms of an order higher than the two-body terms. This patter n is used to provide the estimates of the total nonadditivities in the three trimers within a few percent accuracy.