First-principles study of anatase and rutile TiO_2 doped with Eu ions: A comparison of GGA and LDA+U calculations

摘要

Here, we study some changes on the electronic band structure of anatase and rutile TiO_2 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 4/ 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.