We
have investigated iron-doped rutile TiO<sub>2</sub> in great detail
by density functional theory (DFT) calculations. The influence of
the Fe dopants on the structural and electronic properties are calculated.
Three different dopant models are considered in this study, where
iron is present in Fe(II), Fe(III), and Fe(IV) oxidation states. Our
results indicate that the configuration of Fe(III), where two neighboring
Ti sites are replaced by Fe dopants and an O vacancy locates in between,
is the lowest-energy structure. The resulting Mößbauer
signatures are in excellent agreement with the available experimental
literature data, thus supporting the proposed structural model. Although
the crystal structure of doped rutile is not significantly altered,
even for larger concentrations of dopant atoms, the local structure
around Fe atoms can be strongly distorted, especially due to the presence
of oxygen vacancies. Fe doping lowers the band gap and introduces
midgap states