Density functional theory (DFT) calculations were carried out with the Vienna Ab-initio Simulation Package (VASP) using the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The generation of k-points meshes were done using the Monkhorst-Pack method. The number of k-point divisions along direction i, Ni, was chosen such that Ni × ai ≈ 25 Å for geometric optimizations, ~75 Å for static calculations, with ai being the length of the supercell.