PNNL

Abstract

In this letter we introduce a new variant of the completely renormalized equation-of-motion method with singles, doubles, and noniterative triples (DR-EOMCCSD(T) that employs a novel strategy of handling the cluster product terms that naturally appears in the EOMCC-type expansion for the trial wavefunction. The new parametrization assures required flexibility of the CR-EOMCCSD(T) approach especially in dealing with the challenging excited states primarily dominated by double excitations. As shown on several examples, including the CH+, N2 and C2 benchmark systems, for which the full configuration interaction (FCI) results are available, the new approach is capable of providing the quality of the results that places it among the most efficient approaches accounting approximately for the effect of triples.