Dresden 2014 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 99: Electronic structure theory

HL 99.5: Talk

Thursday, April 3, 2014, 16:00–16:15, POT 151

First-principles study of excitonic effects in Raman intensities — •Yannick Gillet, Matteo Giantomassi, and Xavier Gonze — Université catholique de Louvain, Louvain-la-Neuve (Belgium)

A resonance phenomenon appears in the Raman intensity when the exciting light has frequency close to electronic transitions. The theoretical prediction of the frequency-dependent Raman response of crystalline systems has received little attention.

Indeed, many Raman calculations are nowadays done in the static limit (vanishing light frequency), using Density-Functional Theory and Density-Functional Perturbation Theory, thus neglecting excitonic effects. In this work [1], a finite difference method is used to obtain the frequency-dependent Raman intensity of silicon within the Many-Body Perturbation Theory (excitonic effects are included by solving the Bethe-Salpeter equation). Since the convergence with the sampling of the Brillouin Zone is extremely slow, a double-grid technique needs to be used.

Two main conclusions can be drawn from our analysis. First, the double-grid technique permits to obtain well converged results without requiring huge memory and time requirements. Then, excitonic effects are of crucial importance in the resonance part of the Raman spectrum. The inclusion of these excitonic effects in the computations improves the agreement with the experimental data [2] with respect to analogous results obtained within the independent-particle approach.

[1] Y. Gillet, M. Giantomassi, X. Gonze, Phys. Rev. B 88, 094305 (2013). [2] A. Compaan and H. J. Trodahl, Phys. Rev. B 29, 793 (1984).