where (x A , y A , z A ) is the position of atom A while (x B , y B , z B ) is the position of atom B. r AB is the distance from atom A and B. ϵ is a dielectric constant in a given system. The explicit form of electric field, that is, -∆ϕ is described in supplemental information 3. We should emphasize that atom A is treated as a density while atom B is treated as a point in equation (4). Therefore, r A =(x A , y A , z A ) in equation ( ) is not a single point but a distribution that satisfies ρ A (r A )>0. This ϕ is the electric potential ϕ A that ρ A undergoes. Similarly, atom B is treated as a density while atom A is treated as a point in the equation ( ), and ϕ B is