Nonlocal density functional for the exchange and correlation energy of electrons

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Abstract
A simple nonlocal approximation to the exchange and correlation energies of an inhomogeneous electron gas is developed within the density-functional formalism. A density functional is constructed to give the energy and the linear response of homogeneous systems. We include nonlocal behavior through an ‘‘average density’’ evaluated with the aid of a weight function. By a scaling hypothesis we obtain a universal (i.e., density-independent) differential equation for the weight functions in k space. The functional is applied to the surface jellium model and to light atoms.