Self-consistent image potential in a metal surface

Electron densities and effective potentials at a jellium surface are calculated using the local-density (LD) approximation inside the metal and a physically based interpolation to the image potential outside. The image-plane position $z_0$ is also determined self-consistently, and we find only a slight contraction of $z_0$ with respect to the LD values of Lang and Kohn. We also provide an empirical criterion to determine $z_0$ from the local density.