Regensburg 2025 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 92: Electronic Structure Theory

O 92.4: Vortrag

Donnerstag, 20. März 2025, 15:45–16:00, H25

Electronic excitations in nanostructures from the Bethe-Salpeter equation — •Maximilian Graml, Štěpán Marek, and Jan Wilhelm — Institute of Theoretical Physics and Regensburg Center for Ultrafast Nanoscopy (RUN), University of Regensburg, Regensburg, Germany

Electronic structure calculations are a well-established tool for the identification of candidate materials for technological applications, e.g., in photocatalysis, photovoltaics and energy storage. For the quantitative description of optical properties, many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation (BSE) on top of GW is regarded as the state-of-the-art method.

In this contribution, we present the implementation of the BSE within the open-source package CP2K, enabling the accurate calculation of electronic excitations in molecules and nanostructures. To validate our approach, we benchmark the excitation energies against those obtained with the FHI-aims package.

We further apply our BSE implementation to study electronic excitations in graphene nanostructures, where we investigate the optical absorption spectra and the spatial extent of excited states as a function of nanostructure size. We observe that both properties converge on the scale of 5 nm nanostructure size, guiding experiments towards the rational design of nanostructures in graphene-based optical devices.

Keywords: Bethe-Salpeter equation; electronic excitations; first-principle calculations; nanographenes; quantum chemistry