DFT calculations were performed with GPU-accelerated Quantum ESPRESSO , version 7.2. A plane wave cutoff of 85 Ry (1156 eV) and Monkhorst-Pack sampling of 1 × 1 × 2 k-point grid for structures with only one crepetition and 1 × 1 × 1 grid for structures with more than one c-repetition gave converged energies within 0.001 Ry ( 2 kJ/mol). The structures were relaxed in a variable cell scheme to have forces less than 0.0001 Ry/Bohr ( 0.002 eV/Å) and ∆E tot < 0.00084 Ry ( 1 kJ/mol). The tetragonal symmetry of the structure was retained, as the angles between the crystallographic axes were kept fixed, but the magnitudes of the cell parameters (|a| = |b|, |c|) were varied.