1. Schrödinger E.: Sitzungsber. Preuss. Akad. Wiss.26 (1931) 63.
2. Ziman J. M.: The calculation of Bloch functions,in Solid State Physics, Vol. 26 (eds. H. Ehrenreich, F. Seitz, D. Turnbull). Acad. Press, New York and London, 1971.
3. Pyykkö P.: Relativistic quantum chemistry,in Advances Quant. Chem., Vol. 11 (ed. Per-Olov Löwdin). Acad. Press, New York, 1978, p. 353.
4. Steslicka M.: Progr. Surf. Sci.5 (1975) 157.
5. Glasser M. L.: Amer. J. Phys.51 (1983) 936.