1. Singh, V.A., Zunger, A.: Phys. Rev. B31 (1985) 3729.
2. Fazzio, A., Caldas, M.J., Zunger, A.: Phys. Rev. B32 (1985) 934.
3. Alves, J.L.A., Leite, J.R.: Phys. Rev. B34 (1986) 7174 and references therein.
4. Stoneham, A.M.: Theory of Defects in Solids, London and New York: Oxford Univ. Press 1975.
5. Watts, R.K.: Point Defects in Crystals, New York: Wiley 1977.