Fewest Switches Surface Hopping with Decoherence in the Marcus Inverted Regime: Correct Rates but Wrong Thermal...

Area of Science:

• Quantum dynamics
• Computational chemistry
• Nonadiabatic systems

Background:

• Fewest switches surface hopping (FSSH) is a standard method for simulating nonadiabatic dynamics.
• FSSH typically provides accurate rate constants for the spin-Boson model, often within a factor of two of exact results.
• Augmented-FSSH (AFSSH) incorporates decoherence corrections into the FSSH method.

Purpose of the Study:

• To investigate the accuracy of AFSSH in the deep inverted Marcus regime.
• To analyze the reasons behind AFSSH's performance regarding rate constants and thermal populations.
• To derive an analytical expression for the quantum correction factor in AFSSH simulations.

Main Methods:

• Simulation of nonadiabatic systems using the augmented-FSSH (AFSSH) method.
• Analytical derivation to understand the behavior of AFSSH in the Marcus inverted regime.
• Comparison of AFSSH results with established theoretical predictions.

Main Results:

• AFSSH yields reasonably accurate rate constants in the deep inverted Marcus regime.
• AFSSH produces incorrect thermal populations over a wide range of parameters in this regime.
• The study identifies a resonance between time derivative coupling and exothermicity as the cause for accurate rate constants.
• A self-consistency issue is identified as the reason for incorrect thermal populations.

Conclusions:

• While AFSSH provides accurate rate constants, its thermal populations are unreliable in the deep inverted Marcus regime.
• The analytical derivation clarifies the strengths and weaknesses of AFSSH in specific nonadiabatic scenarios.
• The derived quantum correction factor offers insights for improving AFSSH simulations in the Marcus inverted regime.