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#### Krieger-Li-Iafrate approximation to the optimized effective potential approach in density functional theory for quantum electrodynamics

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##### Fulltext (public)

poster_cecam-hq-epfl_lausanne_switzerland_30th_september_2015.pdf

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##### Citation

Schäfer, C., Flick, J., Appel, H., Pellegrini, C., & Rubio, A. (2015). *Krieger-Li-Iafrate
approximation to the optimized effective potential approach in density functional theory for quantum electrodynamics*.
Poster presented at Green's function methods: the next generation II, CECAM-HQ-EPFL, Lausanne, Switzerland.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0028-2AA3-0

##### Abstract

Many-body perturbation theory (MBPT) opens the possibility to construct approximations to every desired order of a ’weak’ interacting system. The drawback is a in general non-local interaction in space and time and it is therefore a demanding task to apply it to ’real’ systems.
The optimized effective potential (OEP), derived by inversion of the Sham-Schlüter equation, is a natural connection between local density-functional theory and MBPT. In principle, this variationally best local potential reduces the problem to solving a simple system of Kohn-Sham equations combined with the solution of the OEP integral equation. However, converging the full set of OEP equations is a quite challenging procedure and is in practice rarely tackled.
The Krieger-Li-Iafrate (KLI) approximation reduces the integral equation to an analytically solvable one via a dominant orbital approximation. It performs usually quite well for electronic systems.
In the present work, we extend the OEP and KLI approaches to the case of electron-photon interactions in quantum optics and
quantum electrodynamics. Here an effective electronic interaction is transmitted via transversal photons. We present first static
and time-dependent results for the OEP and KLI approximations of the Rabi model and compare with the exact configuration interaction solution and the corresponding exact Kohn-Sham potentials.