Regensburg 2025 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 53: Poster Electronic Structure Theory

O 53.1: Poster

Dienstag, 18. März 2025, 18:00–20:00, P2

Enhancing Efficiency of Bethe-Salpeter equation calculations including spin-orbit coupling — •Seokhyun Hong, Cecilia Vona, Sven Lubeck, and Claudia Draxl — Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin

Calculating optical excitations in materials with significant spin-orbit coupling (SOC) effects is challenging due to the computational costs. We propose a new method to compute optical spectra including excitonic effects within an all-electron framework. This method extends recently introduced second variation with local orbital (SVLO) method[1] towards the Bethe-Salpeter equation (BSE) framework. The SVLO method is based on the conventional second variation (SV) approach for density-funtional theory calculations. In SV, SOC is treated as a perturbation through a two-step procedure. By solving the scalar relativistic (SR) Hamiltonian, we first obtain eigenvalues and states without SOC. A sub-set of these SR Kohn-Sham states is used as basis functions for evaluating the SOC terms. For many materials, this approach can require all available states for convergence and thus may not capture SOC effects accurately without resorting to huge matrix sizes. In the SVLO method, local orbitals (LOs) are included in the SV step as additional basis functions. It could be shown that this enhances the computational efficiency tremendously[1]. Through this work, we have implemented an analogous scheme in the BSE framework. We demonstrate, how we overcome current limitations and achieve highly precise results for materials with strong SOC, such as lead iodide, perovskites, MoS2,etc.

Keywords: Bethe-Salpeter equation; Spin-Orbit Coupling; exciting