Supermolecular approach to manyhyphen;body dispersion interactions in weak van der Waals complexes: He, Ne, and Ar trimers

摘要

Using the diagrammatic manyhyphen;body perturbation theory, various threehyphen;body dispersion terms that appear in the intermolecular Moslash;llerndash;Plesset perturbation theory (MPPT) are identified and classified with regard to the effects of intramonomer electron correlation on the dispersion term. Via the connection with the supermolecular MPPT, it is demonstrated how the leading dispersion nonadditivities arise within supermolecular calculations that employ MPPT or coupled cluster formalisms. The numerical calculations for He3, Ne3, and Ar3in triangular geometries fully confirm theoretical predictions. The calculated values of dispersion nonadditivity clearly show that the coupled cluster theory with single, double, and noniterative triple excitations provides the proper framework for the efficient inclusion of the intramonomer correlation effects in dispersion nonadditivity. The convergence of the twohyphen;body and threehyphen;body terms is shown to be very similar if we compare the threehyphen;body terms of an order higher than the twohyphen;body terms. This pattern is used to provide the estimates of the total nonadditivities in the three trimers within a few percent accuracy.