Density functional theory (DFT) calculations are performed within the projector augmented wave method implemented in the Vienna ab initio simulation package (VASP) employing the PBEsol functional . Calculations employ a plane wave energy cuto↵ of 700 eV. Gamma-centered k -meshes of 6⇥6⇥4 and 6⇥6⇥6 were used for tetragonal and cubic ZrO 2 , respectively. Harmonic phonon calculations were performed using the finite displacement method in PHONOPY with forces calculated using VASP . 3⇥3⇥2 and 2⇥2⇥2 conventional cubic supercells where used for tetragonal and cubic zirconia, respectively.