Generalized Heitler-London theory with exchange energy by the surface integral method: an application to the alkali metal dimer cations

The generalized Heitler-London theory is used to calculate the lowest gerade and ungerade potential energy curves of the alkali metal dimer cations Li2+, Na2+, K2+, Rb2+ and Cs2+. The exchange energy is calculated with the surface integral method and the second order polarization energy by a damped induction series. The results depend only on the properties of the atomic constituents and thus the potentials of all these systems are generated by the same formula without any adjustable parameters. For Li2+ and Na2+ the results agree well with accurate CI calculations. The observed discrepancies for Rb2+ and Cs2+ with previous estimates are discussed.