Electronic Structures of Manganese-Doped Rutile TiO2 from First Principles

DFT (density functional theory) calculations have been carried out to determine the effects of Mn doping to the energy band structures of rutile TiO2, Using the latest improved exchange correlation functional of Wu and Cohen. According to calculations performed on pure rutile, the use of the Wu-Cohen functional leads to improved accuracy in terms of energetic and crystallographic data and energy gap. The Mn effect on energy band structure depends on its occupancy sites in the rutile lattice. Mn substitution of the Ti sites induces significant spin polarization and effective reduction of the energy gap of rutile, with the energy gap being continuously reduced with increasing Mn doping level. Also, quality intermediate energy bands are introduced by moderate levels of substitutional Mn doping, indicating the promise to make use of a wide spectral range of solar irradiance in the visible light regime. On the other hand, interstitial Mn doping results in localized state in the forbidden band, without inducing spin polarization. Oxygen vacancy associated with substitutional Mn leads to similar effects on band structure as that associated with Ti atoms, generating localized defect levels in the forbidden band. Spin polarization can be enhanced by oxygen vacancies associated with the substitutional Mn atoms. The results of this work also indicate the likely potential in using substitutional Mn doping for spintronic applications such as nonvolatile random access memory.