2ND-ORDER EPSTEIN-NESBET CORRECTION TO DYNAMIC CONFIGURATION-INTERACTION ENERGIES

The zero threshold estimate of our dynamic configuration interaction p rocedure, is used to obtain the correlation energy correction for nona ctive electron pairs in multireference configuration interaction treat ments. For exact eigenvectors, the expression is shown to be equivalen t to second order perturbation theory with the Epstein-Nesbet partitio ning of the reference Hamiltonian. We describe our code which has been efficiently implemented on parallel computers. Few tests have been pe rformed, to show the accuracy of our approach by comparison with the r elated multiconfigurational, Moller-Plesset-type treatment. (C) 1996 A merican Institute of Physics.