Confronting surface hopping molecular dynamics with Marcus theory for a molecular donor-acceptor system

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Materials Science

Background:

• Electron transfer (ET) is fundamental to chemical reactions and energy processes.
• Accurate theoretical descriptions of ET are crucial for understanding molecular systems.

Purpose of the Study:

• To evaluate the performance of fewest switches surface hopping (SH) for molecular electron transfer.
• To investigate the influence of system parameters like reorganization energy and electronic coupling on ET dynamics.

Main Methods:

• Utilized a fragment orbital-based SH approach with decoherence correction for simulations.
• Computed SH ET rates across a broad range of timescales (sub-picosecond to nanosecond).
• Analyzed systems with varying reorganization energy (λ), electronic coupling (H_ab), and driving force.

Main Results:

• SH method shows good agreement with semi-classical theory in the non-adiabatic regime.
• Correct scaling of SH ET rate with electronic coupling and reproduction of the Marcus inverted regime were observed.
• In the adiabatic regime, SH ET rates were found to be lower than semi-classical predictions, linked to non-exponential population decay.
• A crossover to femtosecond charge relaxation was observed at high electronic couplings, described by Rabi oscillations.

Conclusions:

• The SH method provides a reliable framework for simulating ET dynamics over extended timescales.
• The study highlights the importance of decoherence and system parameters in adiabatic and non-adiabatic ET processes.
• Findings are relevant for understanding charge transport in organic semiconductors and designing new materials.