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)