1. Ando, K. and Hamaguchi, C. (1975), Phys. Rev. B71, 3876.
2. Balkanski, M. (ed.) (1971) ‘Light Scattering in Solids’, Flammarion, Paris.
3. Balkanski, M., Leite, R.C.C. and Porto, S.P.S. (eds.) (1976) ‘Light Scattering in Solids’, Flammarion, Paris.
4. Birman, J.L. (1965), Phys. Rev. 127, 1093.
5. Born, M. and Huang, K. (1954), ‘Dynamical Theory of Crystal Lattices’, Clarendon Press, Oxford, pp. 89.