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 (linear combination of atomic orbitals) pseudopotential calculations. 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 Localization Function in specific cell regions. The main features of the YBa2Cu3O6 and YBa2Cu3O7 crystals' electron densities are detailed and compared with available experimental data. Since the superconducting transition requires oxidation of the YBa2Cu3O6 crystal, we focused on the electronic rearrangements related to the inclusion of oxygen. Cu-O planes, probably responsible for the superconducting transition, exhibit peculiar electronic properties.