Electronic structure of a high-Tc YBa2Cu3O7 superconductor by a symmetry broken SCF method (Cu4O2)(O4Ba) (Cu4O4)Y(O4Cu4)(O4Ba)(Cu4O2) embedded in an ionic cage

The electronic structure of YBa2Cu3O7 is studied by using cluster approximations. The cluster employed was (Cu4O2)(O-4, Ba)(Cu4O4)Y(O4Cu4)(O4Ba)(Cu4O2), which has D-2h symmetry. The investigation was performed with and without taking into account the crystal field. Results strongly suggest that the holes are located at 2p(pi) of O(1). Calculated excitation energies lie in the four energy regions 1.2-2.0, 2.7-3.2, 3.9-4.0 and 4.6-4.9 eV, which correspond well to the four experimental peaks of visible-near-UV at 1.7, 2.7, 4.1, and 4.7 eV given in previous work. (C) 1998 Elsevier Science B.V. All rights reserved.