Coulomb interaction energy including overlap effects between two one-active electron atoms in various electronic states. Application to the interaction Li(2s)+Li(2s)

Abstract

Formulas for the matrix elements of the first- and second-order Coulomb interaction energy between two one-active electron atoms, either in ground or excited initial electronic states, are displayed for the region of small overlap. The appropriate two-center expansions of the electrostatic potential between two spherical charge distributions are explicitly used for overlapping as well as nonoverlapping regions. Test calculations have been performed for the interaction H(1s)+H(1s) at R=6 and R=8 a.u. The results obtained are in very good agreement with the literature reference values. Calculations have been performed for the first-order electrostatic and second-order induction and dispersion energies for the interaction Li(2s)+Li(2s) in the range 5≤R≤24 a.u. using a set of simple semiempirical functions for the Li atom. The results obtained for the dispersion terms are seen to be in an overall reasonable agreement with recent ab initio values. The increasing importance of both the induction terms and the so-called spherical dispersion terms E00iidisp with the decreasing values of R is emphasized. For the largest dispersion term, the relative contribution of the nonoverlapping and overlapping regions is discussed.