LCPQ

Salle de séminaire IRSAMC

Abstract: 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 electron current density [1]. Using a local-current-density approximation for the exchange-correlation potential we were able to resolve several problems of standard TDDFT, which uses a local-density approximation, at no extra computational cost. For example, we were able to solve the longstanding problem of the overestimation of the static polarizabilities of conjugated polymers.

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 in many-electron systems [2]. Unfortunately this method is computationally demanding which is mainly due to the large number of empty states that have to be taken into account in the standard spectral representations for the self-energy which is the quantity within MBPT that contains all the many-body effects. I will demonstrate how one can reformulate the GW method such that it depends on occupied states only. Our method is general, easy to implement and leads to an immediate speedup of calculations.

[1] G. Vignale & W. Kohn, Phys. Rev. Lett.77, 2037 (1996) [2] L. Hedin, Phys. Rev. 139, A796 (1965)