1. Ekardt, W.: Phys. Rev. B29, 1558 (1984)
2. de Heer, W.A., Knight, W.D.: In Elemental and molecular clusters. Proceedings of the 13th International School, Erice, Italy, July 1?15, 1987. Berlin, Heidelberg, New York: Springer 1991.
3. Yannouleas, C., Broglia, R.A., Brack, M., Bortignon, P.F.: Phys. Rev. Lett.63 255 (1989)
4. Bethe, H.A., Jackiw, R.: Intermediate quantum mechanics, p. 253, 1968
5. Lundqvist, B.I.: Phys. Stat. Sol.32 273 (1969)