Only minor differences of up to 0.06 eV have been observed between the computed values from ReaxFF and DFT-PBE. Our study showed that the hopping process ESB 0 →ESB 1 is preferred to the incorporation of the Na atom into the step-edge via ESB 0 →ESB 1 (Ex.). Due to the higher atomic coordinates, the initial state ESB 0 is thermodynamically more stable than the final state ESB 1 on the upper terrasse.