ELECTRONIC-STRUCTURE OF COPPER OXIDES, VALENCE STATE OF COPPER AND OXYGEN, AND SPIN SPIN COUPLING IN YBA2CU3O7-DELTA AND YBA2CU3O6

A series of electronic states of the clusters, Cu3O12(17-) and Cu3O10(15-) modeling the oxides YBa2Cu3O7-delta and YBa2Cu3O6, respectively, have been calculated by the semiempirical MC SCF method in the INDO approximation. The presence of weak ferromagnetic spin-spin coupling between planes in these crystals has been demonstrated. The chemical bond between planes and chains is very weak - a consequence of electron correlation effects. The Cu atoms in the chains are in the +3 state of oxidation, and those in the planes are in the +2 state.