An energy functional for surfaces

We propose a simple way of correcting general gradient and local density approximation surface energies for errors of these approximations intrinsic to surfaces by the appropriate use of reference systems with an exponential surface potential veff(z)∝e(z/a). A test of this approach applied to general gradient and local density approximation surface exchange energies for half jellium systems removes most of the surface-intrinsic errors and yields excellent results. We suggest that the same procedure would also be successful for surface correlation effects. We conclude with some general remarks about future directions of density functional theory.