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jeudi 18 février — 14:00, attention, horaire exceptionnel

Theoretical spectroscopy from TD Current-DFT and many-body perturbation theory

A. Berger (École Polytechnique)

par Pierre Pujol - 18 février 2010

I will present my work within the frameworks of time-dependent current-density-functional theory (TDCDFT) and many-body perturbation theory (MBPT). TDCDFT is a generalization of time- dependent density-functional theory (TDDFT) in which the key quantity is the current density. Using an exchange-correlation functional derived by Vignale and Kohn we were able to solve several problems of standard TDDFT. We were able to describe excitonic e-ects in the optical spectra of semiconductors, correct the overestimation of static polarizabilities of conjugated polymers and describe the Drude-like tails in the absorption spectra of metals. TD(C)DFT can describe neutral excitations but not excitations in which the total number of electrons change. Therefore, in order to calculate electron addition and removal energies we use MBPT within the GW approximation which is an accurate method that correctly describes the screened electron interaction. Unfortunately this method is computationally expensive which is mainly due to the large number of empty states that have to be taken into account. Therefore we reformulated the GW method such that it depends on occupied states only. Our method is general and can be readily implemented leading to an immediate speedup of calculations. I will also discuss the advantages of extending our approach to real-time propagation.