1. F. García-Moliner and F. Flores, Introduction to the Theory of Solid Surfaces, Cambridge University Press, Cambridge, England (1979).
2. J. E. Inglesfield and B. H. Holland, in: Clean Solid Surfaces (D. A. King and D. P. Woodruff, eds.), Vol. 1, Elsevier, Amsterdam (1981).
3. J. R. Schrieffer, Mol. Cryst. Liq. Cryst.
77, 209 (1981).
4. D. C. Langreth, Phys. Rev. B
5, 2843 (1972).
5. F. Flores and C. Tejedor, J. Phys. (Phys.)
38, 949 (1977).