In this paper, a Self-consistent Orthogonalized linear combination of atomic orbitals (OLCAO) technique with a generalized gradient approximation such as Perdew-Burke-Ernzerhof Solid (GGA-PBE SOL) has been used to scrutinize the structural, optical, electronic and mechanical properties of normal pressure phase (Anatase and Rutile) and high pressure phase i.e., cubic (Fluorite and Pyrite) TiO 2 . Electronic and optical properties of normal pressure phases of TiO 2 are also investigated using (Meta) MGGA-Tran and Blaha (TB09) and obtained results are a close approximation of experimental data. It is seen that the virtually synthesized structural parameter for cubic and tetragonal phases of TiO 2 are consistent with experimental and theoretical data. From the effective mass of charge carriers (m * ), it can be observed that pyrite TiO 2 is having lower effective mass than the fluorite and hence shows higher photocatalytic activity than fluorite. Furthermore, it is seen that fluorite is more dense than anatase, rutile and pyrite TiO 2 . From the theoretical calculations on the optical properties, it can be concluded that optical absorption occursin the near UV region for high and normal pressue phases of TiO 2 . Again from the reflectivity characteristics R(ω), it can be concluded that TiO 2 can be used as a coating material. Elastic constants, elastic compliance constants, mechanical properties are obtained for anatase, rutile, fluorite and pyrite TiO 2 . A comparison of the results with previously reported theoretical and experimental data shows that the calculated properties are in better agreement with the previously reported experimental and theoretical results.

In this paper, the effect of pressure on various properties of brookite and rutile TiO 2 has been investigated along with a phase transition study. It is seen that brookite gets transformed to rutile TiO 2 at 5 GPa pressure. The bandgap of brookite and rutile TiO 2 are direct in nature with values of 3.41 eV and 2.98 eV. Pressure-dependence of the Elastic compliance coefficients, elastic stiffness coefficients, bulk modulus, shear modulus, Young modulus, Poisson's ratio, B/G ratio, Vickers hardness, Lame constant has been calculated at 0, 3, 5 GPa pressures for brookite TiO 2 and at 0, 5, 10, 15, and 20 GPa pressures for rutile TiO 2 . The shear anisotropy factors (A 100 , A 010 , and A 001 ) along {100}, {010}, and {001} planes have been estimated at different pressure for brookite TiO 2 as well as the shear anisotropic factors along {100} and {001} shear planes is estimated for rutile TiO 2 . Moreover, anisotropy factors (A B ), (A G ), and (A U ) have been estimated at different pressure for brookite TiO 2 and rutile TiO 2 . Furthermore, the dielectric constant is determined to investigate other optical properties for both the structures at different pressures. A pretty good agreement has been obtained between our findings and experimental data.

This work investigates the consequences of various exchange correlations on brookite titanium dioxide's (TiO 2 ) structural, electronic, and optical properties. For the first time, statistical analysis of the obtained result compared to experimental data is done to find the best methods for numerous properties. It provides an in-depth study on brookite TiO 2 by implementing OLCAODFTLBFGS algorithms along with GGA-PBE, GGA-PBES, GGA-PW91, GGA-BPW91, GGA-BP86, MGGA-TB09, and Hubbard U parameters to find out multiple properties. Investigated lattice parameters using GGA-PBES shows 0.43%, 0.56%, and 0.09% variation with experimental data, which further improved as 0.08%, 0%, and 0.21%, including Hubbard U parameter in the calculations. E g using OLCAO-MGGA-TB09 shows no variations with the experimental value. Obtained range of absorption offers good agreement with experimental spectra. The statistical analysis using different methods for various properties described here can help find the best suitable ways for other materials. From the analyzed results, it revealed that GGA-PBES+U gives improved structural properties, whereas OLCAO-MGGA-TB09 gives an improvement in electronic properties. DFT provides good results for optical properties than DFT+U.

In this paper, a detailed study and analysis on the electronic and optical properties of anatase, rutile and brookite titanium dioxide (TiO2) which are the naturally occurring phases of TiO2 have been carried out. We have obtained these properties using the self-consistent orthogonalized linear combination of atomic orbitals with meta-generalized gradient approximation (MGGA) and Tran and Blaha (TBO9) as exchange–correlation under the framework of density functional theory. Obtained results on band gap value (E g), dielectric constant and refractive index as calculated by considering the optimal value of c (system-dependent parameter) have been analyzed statistically and are found to be much closer to the experimental values and are better than the other approaches published in the literature. It is seen that optical absorption for all the three phases of TiO2 occurs in UV region of EM spectrum. Using statistical analysis in correlation with other effective methods such as mBJ, GGA + U, GGA + Ud + Up, LSD + U, GW and HSE06 functional, it is found that MGGA-TB09 gives a better description of electronic structure and optical properties with less computation time. This work provides good understanding of electronic and optical properties of TiO2, stems a foundation for its possible applications in photo catalytic activities of dye sensitized solar cells.

No abstract