1. Miller, K. J., Ruedenberg, K.: J. chem. Physics 48, 3418 (1968). This paper contains the most recent and most sophisticated APSG-treatment, a large number of references to earlier papers on the APSG-approximation.
2. Frenkel, J.: Wave Mechanics, Oxford: University Press 1933?1934.
3. Das, G., Wahl, A. C.: J. chem. Physics 44, 87 (1966).
4. Veillard, A., Clementi, E.: Theoret. chim. Acta (Berl.) 7, 133 (1967).
5. Hinze, J. A., Roothaan, C. C. J.: Progr. Theoret. Phys. 40, 37 (1967).