Cluster model calculations of the solid state materials electron structure

Materials of the general composition ACuO2 are the parent compounds of so called infinite layer superconductors. In the paper presented the electron structure of the compounds CaCuO2, SrCuO2, Ca0.86Sr0.14CuO2 and Ca0.26Sr0.74CuO2 were calculated. The cluster models consisting of 192 atoms were computed using quasi relativistic version of semiempirical INDO method. The obtained results indicate the strong ionicity of Ca/Sr-O bonds and high covalency of Cu-bonds. The width of energy gap at the Fermi level increases as follows: Ca0.26Sr0.74CuO2 < Ca0.86Sr0.14CuO2 < SrCuO2 < CaCuO2. This order correlates with the fact that materials of the composition CaxSr1-xCuO2 have have the high temperatures of the superconductive transition (up to 110 K). Materials partially substituted by Sr2+ have also the higher density of states in the close vicinity at the Fermi level that ai the additional condition for the possibility of superconductive transition. It was calculated the strong influence of the vibration motions to the energy gap at the Fermi level. (authors). 1 tabs., 2 figs., 10 refs