1. See, for instance, D. Pines, The Many-Body Problem (W.A.Benjamin, New York, 1961), and the excellent collection of reprints included therein.
2. R. H. Victora, L. M. Falicov and S. Ishida, Phys. Rev. B 30, 3896 (1984).
3. A. Liebsch, Phys. Rev. Lett. 43, 1431 (1979).
4. A. Liebsch, Phys. Rev. B 23, 5203 (1981).
5. M. S. Hybertsen and S. G. Louie, Phys. Rev. B 35, 5585, 5602 (1987).