INVESTIGATION OF THE MANY-PARTICLE SPECTRUM OF SUPERCONDUCTOR YBA2CU3O7

We investigate the electronic structure of superconductor YBa2Cu3O7 through a molecular cluster approach. The calculations are performed self-consistently through a semi-empirical LCAO technique, and correlation effects are taken into account by a configuration interaction procedure (INDO-CI). Our results for the larger clusters yield a density of states (in the valence band) that is in good agreement with the experimental data. We obtain for the ground-state a strong p-d covalency, resulting in a width of around 8 eV for the valence band. The interactions of Cu(1) and (2) with O (1),(2),(3) and (4) are analysed, showing how hybridization occurs. In all cases we calculate the Mott-Hubbard energy U taking into account many-body effects.