We employed a simulation model consisting of 16∆x × 16∆x × 16∆x grids (∆x = 0.3 Å). We set a single Na+ atom at the center of this model, which was converted into density with σ = 0.3 Å. Then, we applied the x-directional homogeneous electric field E x = 1.0 × 10 7 V/m.