An efficient protocol for excited states of large biochromophores

Feighan, Oliver; Manby, Frederick R.; Bourne-Worster, Susannah

Abstract

Efficient energy transport in photosynthetic antenna is a long-standing source of inspiration for artificial light harvesting materials. However, characterizing the excited states of the constituent chromophores poses a considerable challenge to mainstream quantum chemical and semiempirical excited state methods due to their size and complexity and the accuracy required to describe small but functionally important changes in their properties. In this paper, we explore an alternative approach to calculating the excited states of large biochromophores, exemplified by a specific method for calculating the Qy transition of bacteriochlorophyll a, which we name Chl-xTB. Using a diagonally dominant approximation to the Casida equation and a bespoke parameterization scheme, Chl-xTB can match time-dependent density functional theory’s accuracy and semiempirical speed for calculating the potential energy surfaces and absorption spectra of chlorophylls. We demonstrate that Chl-xTB (and other prospective realizations of our protocol) can be integrated into multiscale models, including concurrent excitonic and point-charge embedding frameworks, enabling the analysis of biochromophore networks in a native environment. We exploit this capability to probe the low-frequency spectral densities of excitonic energies and interchromophore interactions in the light harvesting antenna protein LH2 (light harvesting complex 2). The impact of low-frequency protein motion on interchromophore coupling and exciton transport has routinely been ignored due to the prohibitive costs of including it in simulations. Our results provide a more rigorous basis for continued use of this approximation by demonstrating that exciton transition energies are unaffected by low-frequency vibrational coupling to exciton interaction energies.

Citation

Feighan, O., Manby, F. R., & Bourne-Worster, S. (2023). An efficient protocol for excited states of large biochromophores. The Journal of Chemical Physics, 158(2), https://doi.org/10.1063/5.0132417

• Journal Article Type: Article
• Acceptance Date: Dec 11, 2022
• Online Publication Date: Jan 10, 2023
• Publication Date: Jan 14, 2023
• Deposit Date: Jan 27, 2025
• Journal: The Journal of Chemical Physics
• Print ISSN: 0021-9606
• Electronic ISSN: 1089-7690
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 158
• Issue: 2
• DOI: https://doi.org/10.1063/5.0132417
• Public URL: https://durham-repository.worktribe.com/output/3353436