1. Cf. e.g. 5th International Symposium on Small Particles and Inorganic Clusters, 10?14 September 1990, Konstanz, Federal Republic of Germany
2. Knight, W.D., Clemenger, K., Heer, W.A. de, Saunders, W.A., Chou, M.Y., Cohen, M.L.: Phys. Rev. Lett.52, 2141 (1984)
3. Ekardt, W.: Phys. Rev. B29, 1558 (1984)
4. Koutecký, J., Bona?i?-Koutecký, V., Boustani, I., Fantucci, P.: In: Elemental and molecular clusters, p. 214, Benedek, G., Martin, T.P., Pacchioni, G. (eds.) Berlin, Heidelberg, New York: Springer 1987
5. Knight, W.D.: Solid State Phys.40, 93 (1987)