Non-adiabatic Dynamics Simulation of Coupled Exciton and Charge Transfer Processes in a Bacterial LH1-RC Complex

• Applicant: Dr. Sayan Maity
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces ; Biophysics ; Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567892407

Excitation energy transfer in light-harvesting (LH) complexes is a fundamental process in photosynthesis. The objective of the proposal is to develop and implement a novel non-adiabatic simulation approach to study the energy transfer process in LH complexes. By incorporating quantum mechanical/molecular mechanical (QM/MM) methods, the chromophores will be treated by an "on-the-fly" mixed quantum-classical technique such as eXcitonic state-based Surface Hopping (X-SH) while the surrounding protein environment will be described classically allowing for an accurate representation of electronic excited states and their coupling to the protein environment. This innovative approach termed as QM(X-SH)/MM will employ an "on-the-fly" Hamiltonian, surpassing current state-of-the-art methods in the study of biological LH complexes where a pre-defined Hamiltonian is considered to study spectroscopy and ultrafast processes. The key objectives are to apply coarse-grained electronic structure methods for chromophore site energies, ground state energies, and gradients, while incorporating fast electrostatic calculations for the protein environment. This significantly reduces computational costs while maintaining accuracy, making it a practical option for large-scale non-adiabatic simulations of biosystems. This novel method will allow for the simultaneous treatment of exciton propagation and dissociation into charges, a capability currently lacking in the biological light-harvesting research community. Moreover, it will allow applications to systems of hundreds of chromophores which is not feasible with the current state-of-the-art nonadiabatic molecular dynamics implementations. Our research will be focused on the LH1-RC complex of purple bacteria, serving as a model system for exciton transfer and charge separation processes. The overall aim is to investigate the functions of the LH1 and reaction center (RC) complexes during the energy transfer process. Ultimately, the QM(X-SH)/MM approach will serve as a powerful tool to unravel the complex dynamics underlying energy and charge transfer processes in biological systems, facilitating the development of sustainable energy technologies inspired by nature’s photosynthetic machinery.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Dr. Jochen Blumberger