of 400 eV and a 6×6×6 Γ-centered k-point grid was used for a 10-atom primitive cell, ensuring convergence of total energy within 1 meV/atom using vaspup2.0. The cutoff was increased to 520 eV during geometry optimizations to avoid Pulay stress. To account for Van der Waals dispersion interactions, the D3 correction of Grimme et al.