Non-local-density based self-consistent surface calculations. I. Thomas-Fermi lives

An alternative to a local density formula for incorporating the exchange and correlation potential in surface and interface calculations is suggested and examined. To illustrate its use, a simple extended Thomas-Fermi solution for the surface is derived and shown to incorporate the basic physical features expected. At high metallic densities (r s =2-3) it gives close agreement with the charge density and potential obtained by the local density methods.