Point defects are simulated in a 4×4×3 supercell (192 atoms in perfect structure), using a 1×1×1 k-point grid and a plane wave cutoff of 800 eV. All atoms were fully relaxed until residual force smaller than 0.01eV/Å, with lattice parameters fixed. For charged defect, a uniform compensating charge background is added to keep charge neutralization.