A DRESSING FOR THE MATRIX-ELEMENTS OF THE SINGLES AND DOUBLES EQUATION-OF-MOTION COUPLED-CLUSTER METHOD THAT RECOVERS ADDITIVE SEPARABILITY OF EXCITATION-ENERGIES

The concept of intermediate effective Hamiltonians is employed to modify the equation-of-motion coupled-cluster method with singles and doubles (EOM-CCSD). The main goal is to eliminate the extensivity error that plagues the standard formulation of EOM-CCSD. Modification of the EOM-CCSD matrix elements (that will be called dressing here) not only eliminates the size-extensivity error but also gives some approximation to contributions from the triply excited configurations. © 1995 American Institute of Physics.