Electronic and optical properties of anatase TiO2

First-principles calculations using the full-potential linearized augmented plane-wave method have been performed to investigate detailed electronic a nd optical properties of TiO2 in the anatase structure. The fully optimized structure, obtained by minimizing the total energy and atomic fords, are i n good agreement with experiment. Stabilization of the structure by the tra de off between a favorable coordination in the sp(2) hybridization and the Coulomb repulsion among oxygen atoms is also demonstrated. We calculate ban d structure, densities of states and charge densities, and interpret their features in terms of the bonding structure in the molecular orbital picture . The optical properties, calculated within the dipole approximation, are f ound to agree with recent experiments on single crystals of anatase TiO2. N ear the absorption edge, the results show a significant optical anisotropy in the components parallel and perpendicular to the c axis. We demonstrate that this large dichroism results from the existence of nonbonding d(xy) or bitals located at the bottom of the conduction bands, which allows direct d ipole transitions dominantly for the perpendicular component.