The DFT calculations are based on self-consistent, periodic density functional theory using the Vienna Ab-initio Simulation Package (VASP). The BEEF-VdW exchange-correlation functional with projector augmented wave (PAW) pseudopotentials is employed. A dipole layer is applied in the vacuum to eliminate the electrostatic interaction errors between mirror image slabs. A k-point grid of 2×2×1 is used based on Monkhorst-Pack k-sampling, and the convergence of the binding energy with respect to the k-point set is confirmed. A cutoff energy of 400 eV and a force-convergence criterion of 20 meV Å -1 for local energy minimization are used. The climbingimage nudged-elastic-band (CINEB) method with seven intermediate images is used to locate the geometry of transition states , with initial guesses generated using the Image Dependent Pair Potential tool. After the CINEB calculations converge to a force below 80 meV Å -1 for each image, the Lanczos diagonalization approach is employed to refine the transition state. The forceconvergence criterion of the Lanczos optimizations is 40 meV Å -1 .