EVALUATION OF THE VOLUME EFFECT IN THE CORE-CORE INTERACTION ENERGY FOR ALKALI DIATOMICS

The core-core interaction energy other than the point-charge term in t he alkali diatomics is calculated with an ab quantum chemical method. This energy proves to vary as a function of the valence environment. I t is purely repulsive for the cores frozen to the free atomic state, a nd it shows a shallow potential well for (A(2))(2+) or (AA')(2+). The algebraic mean value between those two extreme conditions is recommend ed for adding to the valence energy calculated with the large-core (re lativistic) effective potential without the core-polarization operator . For the large-core effective core potential with the core-polarizati on operator, the volume effect of the core-core interaction calculated from the cores frozen to the free atomic state should be added. (C) 1 997 Academic Press.