Investigating the Energetic Ordering of Stable and Metastable TiO2 Polymorphs Using DFT plus U and Hybrid Functionals

Prediction of transition metal oxide BO2 (B = Ti, V, etc.) polymorph energetic properties is critical to tunable material design and identifying thermodynamically accessible structures. Determining procedures capable of synthesizing particular polymorphs minimally requires prior knowledge of their relative energetic favorability. Information concerning TiO2 polymorph relative energetic favorability has been ascertained from experimental research. In this study, the consistency of first-principles predictions and experimental results involving the relative energetic ordering of stable (rutile), metastable (anatase and brookite), and unstable (columbite) TiO2 polymorphs is assessed via density functional theory (DFT). Considering the issues involving electron-electron interaction and charge delocalization in TiO2 calculations, relative energetic ordering predictions are evaluated over trends varying Ti Hubbard U-3d or exact exchange fraction parameter values. Energetic trends formed from varying U-3d predict experimentally consistent energetic ordering over U-3d intervals when using GGA-based functionals, regardless of pseudopotential selection. Given pertinent linear response calculated Hubbard U values, these results enable TiO2 polymorph energetic ordering prediction. Hybrid functional calculations involving rutile-anatase relative energetics, though demonstrating experimentally consistent energetic ordering over exact exchange fraction ranges, are not accompanied by predicted fractions, for a first-principles methodology capable of calculating exact exchange fractions precisely predicting TiO2 polymorph energetic ordering is not available.