In the case of ZrO 2 also, F QHA alone fails to describe the tetragonal-to-cubic phase transition at all. The tetragonal phase always has a lower free energy than the cubic phase without any correction. If F anh is accounted for, then the cubic phase has lower free energy than the tetragonal phase when it becomes dynamically stable between 2000 K and 2500 K. (see Figure ). This is an intriguing outcome because a similar but more methodical study of ZrO 2 entirely within the self-consistent phonon theory did not predict the transition with the tetragonal phase always having a lower free energy than the cubic phase . Its main differences from our study are the method of TD phonon generation and the application of an additional, higher-order free energy correction. The discrepancy between the two results is a testament that the temperature of phase transition, and whether or not it even occurs, is sensitive to even relatively small uncertainties in energy (DFT, harmonic, or anharmonic).