Görling was the first to point out that we can use Poisson's equation to define an effective charge density from the Kohn-Sham potential. Then, the Laplacian of the Kohn-Sham Hartree-exchange-correlation (Hxc) potential v Hxc (r) defines unambiguously an effective charge density ρ rep (r) whose Coulomb potential is the Hxc potential: