Polaronic effects in the Density Functional Theory for Superconductors

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Density functional theory of superconductivity has been rather successful in predicting material-specific properties, such as the critical temperature Tc, of conventional (BCS-type) superconductors. For the high-Tc cuprates, however, the presently available approximations of the xc free-energy functional fail to give the correct description. The goal of the proposed research is to construct and implement improved approximations of the xc functional by taking polaronic contributions into account. This is achieved by employing diagrammatic techniques of many-body perturbation theory. A dressed (polaronic) Greensfunction is obtained from solving a Dyson equation with a GW-type self-energy. This Greensfunction is then used as basic element in the diagrammatic construction of the xc free-energy functional. This construction is to be viewed as a first step towards a first-principles description of high-T−c superconductors.