DISSOCIATION-ENERGIES WITHIN SELECTED CONFIGURATION-INTERACTION AND PERTURBATION-THEORY

Selected configuration interaction (CI) calculations and second-order perturbational theory are used to truncate systematically multireferen ce single and double excitation CI (MRCI) expansions in the calculatio n of the bond dissociation energies of several systems like the single -bonded LiF molecule or the multiple-bonded N2, NO and O2 diatomic sys tems. The method is extended to compute the CH bond dissociation energ y of ethene C2H4. It is shown how the proposed scheme (perturbation-se lected MRCI (MRCI-PS)) is able to reproduce the accuracy of complete M RCI expansions with only a small number of configurations variationall y evaluated.