Laboratoire des Solides Irradiés, Ecole Polytechnique, 91128 Palaiseau cedex, France

Mardi, 7 décembre 2010,

14 h 00 Salle RAPHAEL 2&3

site d Ivry-sur-Seine

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.
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 quanity 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 and W. Kohn, Phys. Rev. Lett.77, 2037 (1996)

[2] L. Hedin, Phys. Rev. 139, A796 (1965)