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arXiv · 2005.01857

Non-linear response in the cumulant expansion for core hole photoemission

Marilena Tzavala·Joshua J. Kas·Lucia Reining·John J. Rehr
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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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Marilena Tzavala, Joshua J. Kas, Lucia Reining, John J. Rehr. 2020-05-04. Non-linear response in the cumulant expansion for core hole photoemission. https://doi.org/10.1103/physrevresearch.2.033147

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