Spin component scaling in multiconfiguration perturbation theory

Abstract

We investigate a term-by-term scaling of the second order energy correction obtained by perturbation theory (PT) based on a multiconfiguration wavefunction. The total second order correction is decomposed into several terms, based on the level and spin pattern of the excitations. In particular, same spin and different spin double excitations are grouped separately in the spirit of spin component scaling (SeS). Identification of the excitation level is facilitated by the pivot determinant underlying the multiconfiguration PT framework. Scaling factors of the individual terms are determined from the stationary condition of the total energy calculated up to order three. In the single reference framework this procedure has been shown to result scaling factors similar to those applied in Grimme's SeS-M011er-Plesset method. Several decomposition schemes are tested numerically on the example of bond dissociation profiles. We conclude, that the success of spin component scaling at around equilibrium geometries is not right away transferable to the entire potential surface, even if adopting a multireference based PT formulation