ANISOTROPY OF THE BAND-STRUCTURE IN YBA2CU3O7 FILMS - A CLUSTER CALCULATION

In this study the energy spectrum of YBa2Cu3O7 (YBCO) is evaluated usi ng a semiempirical calculation method of the type extended Debye-Hucke l approximation. To simulate the irregular morphology of YBCO films th e structures used in the calculations are formed by several unit cells stacked either along a or along c. The formation of anomalous energy levels arising from irregular atomic arrangements is observed. The phy sical origin of these levels is a mechanism of charge 'spill-out', lea ding to charge transfer and charge hybridization.