The terrace (T) diffusion barriers are in excellent agreement between ReaxFF and DFT-PBE. We found the hopping process T 0 ↔T 1 with an activation energy of 0.05 eV (ReaxFF: For the step-edge (S) structures, the developed reactive force field can adequately recreate the different diffusion processes. Here, hardly any activation barrier was found for the diffusing Na adatom along the step-edge (S 0 ↔S 1 ). Its activation energy of 0.06 eV (ReaxFF: 0.06 eV)