Irregular grid point (x, y, z) is projected to surface point (x0, y0, z0). Note that the projection direction is along the gradient direction at (x0, y0, z0), that is, it is perpendicular to the molecular surface. Here, the hollow circles are inner-side grid points in the low dielectric constant region and the solid circles are outer-side grid points in the high dielectric constant region. The dash line represents the molecule surface. [Color figure can be viewed at wileyonlinelibrary.com]