Scaling in second-order electron correlation calculations. II

Abstract

For pt.I see ibid., vol.12, p.L135 (1979). The method of scaling in second-order electron correlation calculations is extended to take account of the importance of triply excited and quadruply excited configurations in the perturbative expansion of the correlation energy with respect to a single-determinantal reference function for a closed-shell system. It is shown that the scaling parameter may be chosen so that these higher order components of the correlation energy may be neglected. The results of prototype calculations for the molecules CH4, NH3, OH2, FH and N2 are presented.