Electronic structure modulation in Fe- and Ag-doped rutile TiO₂: A GGA+U approach for optoelectronic and solar applications

In this work, we carry out an ab initio study of pure and doped rutile TiO₂ using the GGA+ U the generalized gradient approximation plus Hubbard U correction approach within density functional theory (DFT). Doping with iron (Fe) and silver (Ag) is investigated to understand their effects on the structural and electronic properties, especially the band gap. A comparative analysis is conducted between the different atomic species (Ti, Fe, Ag, and O) to identify the orbitals responsible for the observed band gap narrowing. The results highlight significant modifications in the electronic structure upon doping, including the appearance of states near the Fermi level and noticeable change in the Fermi surface topology, reflecting a different distribution of conducting states that can be tailored for specific functionalities.