Berlin 2012 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 17: Poster Session

MM 17.7: Poster

Monday, March 26, 2012, 17:00–19:00, Poster B

Ab-Initio Hamiltonian and Hedin's Equations for Phonon-Induced Effective Electron-Electron Interaction — •Ronald Starke — Department of Computational Materials Physics, Uni Wien, Sensengasse 8/12, A-1090 Wien, Austria

Ab-initio methods are usually applied to electronic structure theory with an electron-electron interaction given by the Coulomb potential. Nonetheless, it is well-known that the nuclear degrees of freedom (regrouped as phonons) lead to a broad range of effects from modifications in the optical spectra up to superconductivity. On a fundamental level, the phononic degrees of freedom constitute a physical system in its own right. Hence, the total system cannot be described by a purely electronic Hamiltonian. As a first approximation, one disregards the phononic degrees of freedom by taking them into account through an effective electron-electron interaction. This gives rise to a huge field of effective models, the most prominent being BCS theory. However, these effective models clearly do not match the standards of ab-initio electronic structure calculations: not only is the effective phonon-induced electron-electron interaction not parameter free, even worse, important ingredients of the fundamental ab-initio electronic Hamiltonian like the Coulomb potential are not taken into account. We review how this problem can be overcome by the addition of an phonon induced effective but ab-initio electron-electron interaction to the standard ab-initio Hamiltonian and discuss the corresponding modified Hedin equations.