1. See, e.g., Washington, M.A., Genack, A.Z., Cummins, H.Z., Bruce, R.H., Compaan, A., Forman, R.A.: Phys. Rev. B15, 2145 (1977)
2. Values of ionic radii are given by several authors: Cu+:r=0.96 � (Pauling, Ahrens), O2?:r=1.32 � (Goldschmidt),r=1.40 � (Pauling, Zachariasen) see Pauling, L.: The nature of the chemical bond. New York: Cornell University Press (1960). The sum of the ionic radii of Cu+ and O2? is 2.28 (2.36) �, the Cu?O, distance in Cu2O is 1.85 �
3. Dahl, J.P., Switendick, A.C.: J. Phys. Chem. Solids27, 931 (1966)
4. Kleinman, L., Mednick, K.: Phys. Rev. B21, 1549 (1980)
5. Robertson, J.: Phys. Rev. B28, 3378 (1983)