Structural, Elastic and Optical Properties of Ag-Doped Rutile TiO₂

The structural, elastic and optical properties of Ag-doped rutile TiO2 are studied using the first principles calculations method. Four different functionals are employed using the ultrasoft pseudopotentials (USPs) on a supercell of size 2a × 2b × 1c. The band gaps of un-doped TiO2 obtained using PBE, RPBE, PW91 and LDA-CA-PZ are 1.861, 1.873, 1.857 and 1.854 eVs respectively. However, after Ag substitution in the supercell, the band gaps are reduced for all of the functionals. After substitution, in the region near to the Fermi level, some new electronic states are observed. The calculated elastic constants show that the structure is mechanically stable. The obtained values of the B, G and elastic constants of un-doped TiO2 are consistent with prior published experimental findings. For Ag-doped supercell, implementing PW91, B and G are 119 and 62 GPa. For the same size of supercell, using LDA-CA-PZ, B and G are 152 and 70 GPa. Besides, the results of the optical properties show that the major absorption peaks for all of the functionals locate away from the visible region. This shows poor absorption of visible light and weak photocatalytic activity of rutile TiO2.