Elastic, electronic and optical properties of anatase TiO₂ under pressure: A DFT approach

The first principle pseudopotential method within the generalized gradient approximation (GGA) and the local density approximation (LDA) have been applied to investigate the electronic, elastic and optical properties plus the acoustic wave velocities of anatase TiO₂ under high pressure (0–80 GPa). The calculated bulk moduli (177 GPa and 181 GPa) are in excellent agreement with experimental results (179 GPa and 178 GPa). Anatase TiO₂ is found to be mechanically stable under high pressure (0–80 GPa) by applying the Born stability criteria. Acoustic wave speeds are predicted in the [100], [010], [001],[11¯0], [110] and [101¯] directions by using the calculated elastic constants. An underestimated band gap (2.174 eV (GGA), 2.113 eV (LDA)) is obtained, and it shows no change when the pressure is varied from 0–10 GPa. The bandgap reduction is caused by the decrease of the lattice constants and volume and an increase of the internal parameters as a function of pressure. The dielectric constant ε (ω) and the refractive index show a good agreement with the experimental results. From the absorption spectrum, it is found that the photocatalytic activity of anatase TiO₂ decreases with an increase of pressure. The pressure effect on the energy loss function appears in the form of new peaks in the energy loss spectra.