Calculation Study On The Band Structures Of Doped Titanium Dioxide

Due to the outstanding chemical stability, anti-abrasion, low-cost and nontoxic, has been one of the most potential materials for photocatalytic. However, a high intrinsic band gap of TiO2 allows only absorption of the ultraviolet part of the solar irradiation. In order to extend optical absorption of the TiO2 in solar spectrum, several approaches such as doping of various atoms have been proposed. Depend on the modern computational simulation methods, we calculated the effects of TiO2 doped with B,C,N,F,S,V,Fe,Ni.In this thesis, we introduced the development and application of computational simulation methods that applied in materials research field, and the First-principles method was discuss in detail. Some important concepts, such as Density Functional Theory (DFT), Local Density Approximation (LDA), Generalized Gradient Approximation (GGA), were explained. The function and application of CASTEP software pack, which was employed in this experiment, was also presented.A mathematic model of doped TiO2 (ruitle and anatese) with super-cell form was built. The structure was optimized under First-principles method joined with Generalized Gradient Approximation. In that way, we found the stabile structure with lowest energy of doped TiO2. The result showed that the two most important facts to the displacement of doped structure were the symmetry of the doped place and the difference between doped atomic and replaced atomic.Base on the result of structure optimization, the electronic band structure, density of state, and electron-density distributions of doped TiO2 were calculated under First-principles method joined with Local Density Approximation. Depend on the theories of Kuroiwa, the analysis of the electron-density distributions showed that theelectrovalent bond only existed in F-doped TiO2.Combining with the data analysis of band structure and density of state, the position and shape of the doped bands would have great impaction on the optical-response property and photocatalytic performance. When the doped bands located on the top of valence band that composed with O 2p state or located on the bottom of conduction band that composed with Ti 3d state, the band gap would decrease more or less. This kind of band structure wouldn't increase the carrier-recombination centers for the inexistence of center band. Therefore, the researches of S anion doped TiO2 and V doped TiO2 would be feasible and hopeful.