Role of Titanium replacement with Pd atom on band gap reduction in the anatase Titanium Dioxide: First-Principles calculation approach

Titanium dioxide (TiO2) is one of the highly promising energy materials. Nevertheless, it has a wide energy bandgap that restricts its absorption capacity within the visible light spectrum. To investigate the effects of doping the transition-metal Palladium (Pd) into anatase TiO2, we perform first-principles calculations in the framework of density functional theory (DFT). All calculations are carried out in the scheme of Hubbard potential (U) correction to account for the correlated effects in TiO2. For this purpose, the first-principles calculations are carried out with the CASTEP code in the formalism of GGA + U. The Pd-doped TiO2 was examined in detail for its electronic structure, lattice parameters, E-K representation, the density of states and optical properties. The results showed that lattice parameters of TiO2 changed after doping. The band structure, partial density of state (PDOS), total density of state (TDOS), complex dielectric function, refractive index, optical absorption, and energy loss function of Pd-doped anatase are improved drastically. It was observed that the doping process adds Pd 4d electronic states into different energy ranges and thus reduces middle states within the band gap region. Our electronic structure calculations indicate augmentation of d-states around the Fermi level, induced by doping Pd. Additionally, compared with the undoped TiO2, the absorption edges of Pd-doped TiO2 show a shift from the UV spectrum towards the visible light region. The results indicate that the GGA + U approach is unique in determining the real band structure of semiconductors which is close enough to empirical results.