1. The calculation of T can be found in references 2–4.
2. F. Seitz and J.S. Koehler, Solid State Phys. 2, 305 (1956).
3. C.H. Kinchin and R.S. Pease, Report Prog. Phys. 18, 1 (1955).
4. J.W. Corbett and J.C. Bourgoin, Point Defects in Solids, ed. J.W. Crawford and L.M. Slifkin, Plenum Press, New York (l974), vol. 2, chap. 1.
5. N.F. Mott, Proc. R. Soc. A.124, 426 (1929)