The migration of Cl ions correlates well with the change in the potential difference across the simulation cell (Fig. ). The movement of a negatively charged ion towards the surface results in a more positive potential from the increase in polarization. The correlation between the Cl migration towards the positive Au(100) surface and the increase in potential can be clearly seen from the corresponding trajectories. For one of the trajectories of Au(111) at D = 0, the Cl moves towards the other side of gold electrode, which leads to a more negative potential instead.