RELATIVISTICALLY PARAMETRIZED EXTENDED HUCKEL CALCULATION OF NET CHARGES ON ATOMS IN YBA2CU3O7

The electronic structure of YBa2CU3O7 has been investigated by the met hod of relativistically parametrized extended Huckel (REX) calculation s. Calculations have been carried out in steps, for different clusters of atoms, so as to obtain a proper picture of the charge distribution in the solid state. We have calculated the total energies of differen t electronic configurations for each cluster. The bulk has been simula ted as a vast collection of appropriate point charges for each electro nic configuration of the cluster. Interaction of the cluster with its counterion environment has been treated in the point charge interactio n model. The ground-state electronic configuration has then been deter mined for each cluster embedded in solid. These calculations show that on average the hole has a higher probability to reside on the 0(4) at oms and a lower probability to be found in the Cu(1)-O(1) chains. Thes e results are in good agreement with experimental observations.