1. A.D.B. Woods, B.N. Brockhouse, R.H. March, A.T. Stewart and R. Bowers, Phys. Tev. 128, 1112 (1962).
2. B.N. Brockhouse, T. Arase, G. Caglioti, K.R. Rao and A.D.B. Woods, Phys. Rev. 128, 1099 (1962).
3. S.H. Koenig, Phys. Rev. 135A, 1693 (1964).
4. See, for example, W. Cochran and R. Cowley, Handbuch der Physik, Vol XXV/2a, Springer (1967) p. 83f.f. More generally D(q) is not diagonal in G, but in simple metals the off -diagõnal terms are thought to be small.
5. (L. Sham, Proc. Roy. Soc. A283, 33 (1965)). For simplicity of notation we consider only one atom/cell.