Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 78: Frontiers of Electronic Structure Theory: Many-Body Effects on the Nano-Scale V

O 78.8: Talk

Thursday, March 19, 2015, 12:30–12:45, MA 004

Excitonic effects in many-body calculations — •Matteo Gatti^1,2, Igor Reshetnyak¹, Giorgia Fugallo¹, Pierluigi Cudazzo¹, Francesco Sottile¹, and Lucia Reining¹ — ¹LSI, CNRS-Ecole Polytechnique and ETSF, Palaiseau, France — ²Synchrotron Soleil, Gif-sur-Yvette, France

The Bethe-Salpeter equation (BSE) is the state-of-art approach to calculate the absorption spectra of a large variety of materials [1]. Here we show that that the BSE is a powerful and accurate method also for the calculation of the exciton dispersion [2-4] (i.e. the exciton energy as a function of the momentum q carried by the electron-hole pair), and of the off-diagonal elements of the dielectric function in reciprocal space є_G,G′(q,ω) [5]. On the one hand, this allows the ab initio simulation of spectra measured by Electron Energy-Loss Spectroscopy (EELS) and Inelastic X-ray Scattering (IXS), including its Coherent version (CIXS), well beyond the optical limit q→0. On the other hand, this opens the door to the calculation of spectral functions [6-8] using the cumulant expansion for the Green’s function G with a screened Coulomb interaction W that includes excitonic effects beyond the random-phase approximation employed in the GW approximation.

[1] G. Onida, et al., Rev. Mod. Phys. 74, 601 (2002). [2] M. Gatti and F. Sottile, Phys. Rev. B 88, 155113 (2013). [3] P. Cudazzo, et al., Phys. Rev. B 88, 195152 (2013). [4] G. Fugallo, et al., unpublished. [5] I. Reshetnyak, et al., unpublished. [6] M. Guzzo, et al., Phys. Rev. Lett. 107, 166401 (2011). [7] M. Gatti and M. Guzzo, Phys. Rev. B 87, 155147 (2013). [8] M. Guzzo, et al., Phys. Rev. B 89, 085425 (2014).