First-principles study of anatase and rutile TiO2 doped with Eu ions:: A comparison of GGA and LDA+U calculations

Here, we study some changes on the electronic band structure of anatase and rutile TiO2 doped with Eu ions using first-principles calculations. This work presents a comparison of a GGA and LDA+U calculations. It was found that the GGA calculations show better agreement with experimental data than LDA+U calculations. From our study a series of highly localized states in the host matrix band gap was found. According to our calculations, and as it is widely known, these states are mainly Eu 4f character. However, contrary to the common idea that Eu orbitals should be localized as atom-free-like states, our calculations show that Eu orbitals hybridize with the host oxygen and titanium orbitals; the same occurs in the valence band, as well as in the conduction band region.