Similarity-transformed Hamiltonian configuration-interaction

The aim of our similarity-transformed Hamiltonian is to improve the computation of the correlation energy of conventional configuration-interaction (Cl) calculations. In this framework, the conventional wave function is multiplied by the correlation function 14,15,16)... 

Several attempts have been made to remove the pervasive failing of the perturbative CC approximations at large internuclear separations. The representative examples include the externally-corrected SRCC methods (6,10,63-74), the active-space SRCC approaches (14,19, 75-86), the orbital-optimized SRCC methods (39,87,88), and the perturbative CC approaches based on the partitioning of the similarity-transformed Hamiltonian (89,90) (see ref 91 for the original idea). Of all these approaches, the reduced MRCCSD (RMRCCSD) method (68-74), which uses the multi-reference configuration interaction (MRCI) wave Unctions to extract information about triply and quadruply excited clusters, and the active-space CCSDt and CCSDtq methods (19,85,86) and their earlier state-selective (SS) CCSD(T) and CCSD(TQ) analogs (14, 75-84) are particularly promising. The RMRCCSD approach can be used to success-... 

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