Atoms-in-molecules treatment of Li 2 + and Li2 using optimum Gaussian approximations of Li+ and Li eigenstates

Abstract

Expectation energies for the Li+, Li and Li− ground states and for the 1s 22p Li excited state are individually minimized with respect to variation of parameters in Gaussian lobe expansions of the 1s, 2s and 2p AO's. A new technique is used to control 1s–2s orthonormality. The resulting approximate many-electron atomic eigen-functions are utilized for determining interatomic matrix elements in atoms-in-molecules (AIM) calculations on the two lowest energy 1 ∑ states of Li2 and on the lowest energy 2 ∑ g + and 2 ∑ states of Li 2 + . For R greater than 4 a.u., convergence to exact theoretical AIM limits, within about 0.001 h.u., is obtained by using three-term expansions. Three-structure Li2 and two-structure Li 2 + AIM energies are above experimental by 0.005 and 0.007 h.u., respectively. It is conjectured that an AIM model extended to permit scaling of valence electrons independently of innershell electrons would reduce significantly these energy differences.