Calculation and analysis of exciton couplings via a subsystem formulation of the GW-Bethe-Salpeter Equation

2025/11/21 by Sarathchandra Khandavilli, Khandavilli, Sarathchandra, A. Förster +3
Chemistry · Physics and Astronomy · #Advanced Chemical Physics Studies #Chemical Physics (physics.chem-ph) #FOS: Physical sciences #Molecular spectroscopy and chirality #Spectroscopy and Quantum Chemical Studies

paper · pdf · doi:10.48550/arxiv.2511.17077

openalex publication_date 2025/11/21 · openalex created_date 2025/11/25 · openalex updated_date 2026/07/28

Abstract

We present a fragment-based framework for analyzing exciton couplings within the GW-Bethe-Salpeter Equation formalism using localized molecular orbitals, and assess how excitonic states in molecular dimers can be decomposed into local and charge-transfer (CT) sectors. Our localization procedure preserves orbital orthonormality via a block-diagonal unitary transformation, enabling a simple and interpretable analysis of excitonic interactions. Using ethylene and pyrene dimers as model systems, we identify key effects of excitonic basis truncation and coupling approximations on excitation energies. We then extend the method to chlorophyll dimers, where weak CT asymmetries emerge due to geometric distortions. This framework offers a tractable route to analyze excitonic behavior in complex systems and paves the way for future fragment-based reconstruction of full exciton coupling matrices in large molecular assemblies.

Citations

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