Direct-space analysis of the electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals

The electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals is investigated by means of fully periodic Restricted Hartree-Fock LCAO pseudopotential calculations. In order to give a detailed description of the bonding and atomic properties of the materials studied we selected the Quantum Theory of Atoms in Molecules approach, and complementary information is obtained from the analysis of the Electron Localisation Function in specific cell regions. The main features of the YBa2Cu3O6 and YBa2Cu3O7 crystals electron densities are detailed and compared with available experimental data. As the superconducting transition requires oxidation of the YBa2Cu3O6 crystal, we focus on the electronic rearrangements related to the inclusion of oxygen. Cu-O planes, probably responsible for the superconducting transition, exhibit peculiar electronic properties.