SIZE-CONSISTENT SELF-CONSISTENT COMBINATION OF SELECTED CI AND PERTURBATION-THEORY

The present work proposes a consistent combination of two recently rep orted computational schemes, namely a size-consistent selected CI and a non-divergent second-order perturbation evaluation. The method treat s large doubles (and any set of higher excited determinants) in a vari ational manner and the small doubles in a perturbative mode, without a ny unlinked contributions and exactly treating the EPV terms. Strict s eparability into closed-shell subsystems is ensured if the localized M Os are used. The efficiency of our proposal is illustrated by a few ca lculations (NH3 in the DZP basis set, H2O in the DZ basis set and the water dimer 2(H2O)).