An <i>ab initio</i> study of core–valence correlation

Abstract

Including core–valence correlation in ab initio CI calculations results in a contraction of the atomic valence shell, particularly for the first two columns of the periodic table. In addition, including core–valence correlation improves the calculated atomic ionization potentials and the atomic energy separations. For the alkali dimers, Na2, K2, and Rb2, our calculated Re’s are in excellent agreement with experiment when core–valence is included. We find for the alkali dimers that the valence De’s are accurate.