COMPARISON BETWEEN MOLECULAR-ORBITAL AND SURFACE INTEGRAL CALCULATIONS OF THE EXCHANGE ENERGY FOR THE HOMONUCLEAR DIMER IONS HE-2(-2(+) ANDBE-2(+)(), LI)

The exchange energy, defined as half of the energy splitting of the ge rade and ungerade states of a molecular ion, is investigated by molecu lar orbital calculations and by the surface integral method. Numerical results of He-2(+), Li-2(+), and Be-2(+) are obtained through restric ted Hartree-Fock, unrestricted Hartree-Fock and localized Heitler-Lond on type calculations. The results of the surface integral method are a nalytical expressions which depend only on the ionization energy. Whil e the approaches are completely different, the results are generally i n good agreement. Discrepancies are highlighted with the hope of promo ting further interplay of these complementary methods. (C) 1995 Americ an Institute of Physics.