1. J. Simons, J. Phys. Chem. 95 (1991)1017.
2. I. Flemming,Frontier Orbitals and Organic Chemical Reactions (Wiley, London, 1976).
3. R.J. Bartlett, J. Phys. Chem. 93 (1989)1697.
4. R. Ahlrichs and P. Scharf,Ab Initio Methods in Quantum Chemistry, Vol. l, ed. K.P. Lawley (Wiley, 1987), pp. 501?537.
5. B.O. Roos, ibid., Vol. 2, pp. 399?446.