Easily Implementable Nonlocal Exchange-Correlation Energy Functional

An exchange-correlation functional for nonuniform electronic systems is developed which provides an easily implementable correction to the local density approximation. It is applied to metallic surface energies, as well as to self-consistent atomic calculations which include the ground-state energies of a number of atoms, plus the removal energies for $1s$, $2s$, $3s$, $4s$, $2p$, $3p$, and $3d$ electrons. In all cases tried a substantial improvement was found.