1. G. A. Slack, in Solid State Physics, Vol. 34, F. Seitz, D. Turnbull, and H. Ehrenreich, eds. (Academic Press, New York, 1979), pp. 1?71.
2. D. Gerlich and P. Andersson, J. Phys. C Solid State Phys. 15:5211 (1982).
3. P. Andersson, Submitted for publication (1984).
4. G. A. Slack and R. G. Ross, Submitted for publication (1984).
5. R. G. Ross, P. Andersson, and G. Bäckström, Mol. Phys. 38:377 (1979).