Local density approximation for superconductors

A universal LDA-type density functional describing the electronic correlati ons in superconductors is developed from first principles. The functional i s constructed from the exchange-correlation free-energy density, f(xc)(hom) , of a homogeneous electron gas exposed to an external translationally inva riant pairing field. The quantity f(xc)(hom), which is a function of the de nsity and a functional of the induced order parameter, is calculated by man y-body perturbation theory.