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Nonlinear response in the cumulant expansion for core-level photoemission

Abstract : Most currently used approximations for the one-particle Green's function G in the framework of many-body perturbation theory, such as Hedin's GW approximation or the cumulant GW+C approach, are based on a linear-response approximation for the screened interaction W. The extent to which such a hypothesis is valid and ways to go beyond have been explored only very little. Here we show how to derive a cumulant Green's function beyond linear response from the equation of motion of the Green's function in a functional derivative formulation. The results can be written in a compact form, which opens the possibility to calculate the corrections in a first-principles framework using time-dependent density functional theory. In order to illustrate the potential importance of the corrections, numerical results are presented for a model system with a core level and two valence orbitals.
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https://hal.archives-ouvertes.fr/hal-03098580
Contributor : Lucia Reining <>
Submitted on : Tuesday, January 5, 2021 - 6:39:34 PM
Last modification on : Monday, January 18, 2021 - 9:55:05 AM

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PhysRevResearch.2.033147.pdf
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Marilena Tzavala, J. Kas, Lucia Reining, J. Rehr. Nonlinear response in the cumulant expansion for core-level photoemission. Physical Review Research, American Physical Society, 2020, 2 (3), ⟨10.1103/PhysRevResearch.2.033147⟩. ⟨hal-03098580⟩

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