1. A.J. Sievers and S. Takeno, Phys. Rev. Lett. 61 970 (1988).
2. S. Takeno, K. Kisoda and A.J. Sievers, Prog. Theor. Phys. Suppl. No.94, 242 (1988).
3. For a review, see for example, S. Flach and CR. Willis, Phys. Rpts, 295, (1998), 181.
4. For a review, see for example, A.A. Maradudin, E.W. Montroll, G.H. Weiss and LP. Ipatova, Theory of Lattice Dynamicss in the Harmonic Approximation, Academic Press, New York and London, 1971.
5. A.J. Sievers, U.T. Schwartz and L.Q. English, Phys. Rev. Lett. 83 223 (1999).