Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 54: Optical Properties

HL 54.7: Vortrag

Mittwoch, 28. März 2012, 12:30–12:45, EW 203

Bethe-Salpeter Equation in the Tamm-Dancoff Approximation and beyond — •Tobias Sander, Ronald Starke, and Georg Kresse — Computational Materials Physics, University of Vienna, Sensengasse 8/12, 1090, Austria

Within the framework of many body perturbation theory, optical absorption spectra are usually calculated using the GW method followed by a subsequent solution of a Bethe-Salpeter like equation. The second step usually involves several approximations. First, the Green function is represented by a one-particle Green function. Second, in solid state calculations, the coupling between resonant (positive frequency branch) and anti-resonant (negative frequency branch) excitations is usually neglected. This approximation is referred to as Tamm-Dancoff approximation. In this work we (i) discuss an efficient method to remove the Tamm-Dancoff approximation for solids, (ii) apply the new approach to three prototypical systems, Si, LiF and Ar. To this end, the recently suggested quasi-particle GW (QPGW) of Shilfgaarde et al. is used to perform the GW calculations [1], followed by a solution of the BSE [2]. We find that the Tamm-Dancoff approximation underestimates the excitonic binding energy by about 300 meV in LiF and Ar, whereas only negligible changes are observed for Si.

[1] M. van Schilfgaarde, T. Kotani, and S. Faleev, Phys. Rev. Lett. 96, 226402 (2006).
S. Albrecht, L. Reining, R. Del Sole, and G. Onida, Phys. Rev. Lett. 80, 4510 (1998).