Local Density Approximation for Superconductors

A universal LDA-type density functional describing the electronic correlations in superconductors is developed from first principles. The functional is constructed from the exchange-correlation free-energy density, fxcʰᵒᵐ, of a homogeneous electron gas exposed to an external translationally invariant pairing field. The quantity fxcʰᵒᵐ, which is a function of the density and a functional of the induced order parameter, is calculated by many-body perturbation theory.