Polymorphs of Titanium Dioxide: An Assessment of the Variants of Projector Augmented Wave Potential of Titanium on Their Geometric and Dielectric Properties

Titanium dioxide (TiO2) is one of the importantfunctionalmaterials owing to its diverse applications in many fields of chemistry,physics, nanoscience, and technology. Hundreds of studies on its physicochemicalproperties, including its various phases, have been reported experimentallyand theoretically, but the controversial nature of relative dielectricpermittivity of TiO2 is yet to be understood. Toward thisend, this study was undertaken to rationalize the effects of threecommonly used projector augmented wave (PAW) potentials on the latticegeometries, phonon vibrations, and dielectric constants of rutile(R-)TiO2 and four of its other phases (anatase, brookite,pyrite, and fluorite). Density functional theory calculations withinthe PBE and PBEsol levels, as well as their reinforced versions PBE+Uand PBEsol+U (U = 3.0 eV), were performed. It was found that PBEsolin combination with the standard PAW potential centered on Ti is adequateto reproduce the experimental lattice parameters, optical phonon modes,and the ionic and electronic contributions of the relative dielectricpermittivity of R-TiO2 and four other phases. The originof failure of the two soft potentials, namely, Ti_pv and Ti_sv, inpredicting the correct nature of low-frequency optical phonon modesand ion-clamped dielectric constant of R-TiO2 is discussed.It is shown that the hybrid functionals (HSEsol and HSE06) slightlyimprove the accuracy of the above characteristics at the cost of asignificant increase in computation time. Finally, we have highlightedthe influence of external hydrostatic pressure on the R-TiO2 lattice, leading to the manifestation of ferroelectric modes thatplay a role in the determination of large and strongly pressure-dependentdielectric constant.

Automated summary

Titanium dioxide (TiO2) is an important functional material with diverse applications. This study investigated the effects of different projector augmented wave (PAW) potentials on the properties of TiO2 and its phases. The use of PBEsol level and standard PAW potential centered on Ti reproduced the experimental results well. The failure of soft potentials in predicting certain properties was discussed. Hybrid functionals slightly improved the accuracy at the expense of increased computation time. The influence of external hydrostatic pressure on the lattice was also highlighted.