LARGE ATOMIC CORE CORE CORRELATION-EFFECTS

The effects of core-valence and core-core correlation on valence ionization potentials (IP) and excitation energies of Ca+, neutral Sc and Sc2+ are studied. Core-valence correlation has a large effect, particularly on 3d excitations, but results in overestimated (by up to 0.8 eV) IPs. Core-core correlation reduces the effect of core-valence correlation and may reduce the computed IP by as much as 1 eV compared with the core-valence CI result. Computing only the valence and core-valence correlation energy while excluding the core-core contribution in molecules containing Ca and Sc is thus not advisable.