1. For a detailed discussion of the Born-Oppenheimer approximation see, e.g., G. V. Chester, Adv. Phys. 10, 357 (1961).
2. W. Kohn and L. Sham, Phys. Rev. A 140 1133 (1965); for a discussion of the connection between the local density approximation and pseudopotential perturbation theory, see Hafner“ and Hafner and Eschrig.”
3. The first to invent the pseudopotential technique appears to be H. Hellmann, Acta Physico-Chimica URSS 1, 913 (1935); 4, 225 (1936).
4. V. Heine, D. Weaire, and M. H. Cohen, in: Solid State Physics, Vol. 24, Academic Press, New York (1971).
5. For a general review see E. G. Brovman and Yu. M. Kagan, in: Dynamical Properties of Solids (A. A. Maradudin and G. K. Horton, eds.), Vol. 1, North-Holland, Amsterdam (1974).