1. Weaire D. and Thorpe M.F. (1971) Phys. Rev. B4, 2508.
2. Hickey B.J. and Morgan G.J. (1986) J. Phys. C19. 6195.
3. Anderson P.W. (1958) Phys. Rev. 109, 1492.
4. Kramer B. and Weaire D (1979) in “Amorphous Semiconductors”, ed. M.H. Brodsky (Topics in Applied Physics, vol. 36) (Springer-Verlag).
5. Mott N.F. and Davis E.A. (1979) “Electronic Processes in Non-Crystalline Materials” (Clarendon Press).