has the same order of magnitude as the favoured terrace hopping mechanism T 0 ↔T 1 . Also, the attachment process S 2 →S 0 towards the step-edge is highly preferred over its inverse counterpart S 0 →S 2 . While an energy barrier of 0.18 eV (ReaxFF: 0.17 eV) hinders the detachment of the Na atom, the inverse attachment process is almost barrier-free (DFT-PBE: