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arXiv · 2502.05144

Revisiting ab-initio excited state forces from many-body Green's function formalism: approximations and benchmark

Rafael R. Del Grande·David A. Strubbe
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Abstract

Ab initio techniques for studying the optical and vibrational properties of materials are well-established, but only a few recent studies have focused on the interaction between excitons and atomic vibrations. In this paper, we revisit the excited state forces method, based on GW/BSE and DFPT calculations and provide a practical implementation and straightforward workflow. We fixed issues from Ismail-Beigi and Louie's implementation in \textcolor{blue}{Phys. Rev. Lett. 90, 076401 (2003)} and use an approximation for GW-level electron-phonon coefficients that improves our calculations accuracy. We explore its technical aspects, including convergence and the quality of approximations used for CO molecule, LiF and monolayer MoS$_2$. We successfully apply this method to investigate diverse kinds of self-trapped excitons in LiF, including polaronic excitons, discuss excited state relaxation strategies and project excited state forces in phonon displacement to explore exciton-phonon interactions. Our results provide the tools to study exciton-phonon related phenomena in molecules in materials, including coherent phonon generation, such as resonant Raman, self-trapped excitons and excitonic insulators.

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Rafael R. Del Grande, David A. Strubbe. 2025-02-07. Revisiting ab-initio excited state forces from many-body Green's function formalism: approximations and benchmark. https://arxiv.org/abs/2502.05144

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