Electronic structure of high-temperature superconductors. I

The electronic structure of high-Tc copper-based superconductors was studied using the quasirelativistic INDO molecular orbital method. Model clusters of YBa2Cu3Oy systems were investigated for y ranging between 6.0 and 7.0. Monomeric units [Ba8Cu3Ox]q and [Y4Ba8Cu4Ox]q, dimeric units [Ba12Cu8Ox]q as well as tetrameric units [Ba18Cu12Ox]q over 300 valence orbitals were studied. From the set of occupied molecular orbitals the density of states (DOS) function was calculated along with its d-orbital projection. The highest occupied molecular orbitals cover the oxygen p-band whereas the copper d-band lies at lower energies. Superconducting phase models (y=6.75 to 7.0) have a higher d-DOS function at higher energies with respect to the non-superconducting phase (y=6.0). (author). 5 figs., 4 tabs., 10 refs