Abstract
The relative energies of the low-pressure rutile, anatase, and brookite polymorphs and the high-pressure columbite polymorph of have been calculated as a function of temperature using the diffusion quantum Monte Carlo (DMC) method and density functional theory (DFT). The vibrational energies are found to be important on the scale of interest and significant quartic anharmonicity is found in the rutile phase. Static-lattice DFT calculations predict that anatase is lower in energy than rutile, in disagreement with experiment. The accurate description of electronic correlations afforded by DMC calculations and the inclusion of anharmonic vibrational effects contribute to stabilizing rutile with respect to anatase. Our calculations predict a phase transition from anatase to rutile at K.
- Received 20 October 2016
- Revised 26 January 2017
DOI:https://doi.org/10.1103/PhysRevB.95.121108
©2017 American Physical Society