Nonadiabatic dynamics with quantum nuclei: simulating charge transfer with ring polymer surface hopping.

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Materials Science

Background:

• Simulating electronic processes like charge transport requires accounting for non-adiabatic electronic and nuclear quantum effects, especially at low temperatures.
• Existing methods like fragment orbital-based surface hopping (FOB-SH) treat nuclei classically, limiting accuracy for quantum nuclear phenomena.

Purpose of the Study:

• To extend FOB-SH by incorporating nuclear quantum effects using ring-polymer molecular dynamics (RPMD).
• To evaluate three distinct RPMD-based approaches for simulating charge transfer dynamics.

Main Methods:

• Developed and applied three flavors of FOB-SH combined with RPMD: RPSH with bead approximation (RPSH-BA), RPSH with weighted bead approximation (RPSH-wBA), and the isomorphic Hamiltonian method (SH-RP-iso).
• Investigated hole transfer in a molecular dimer model, analyzing detailed balance, internal consistency, and temperature/driving force dependence.

Main Results:

• RPSH-BA underestimated excited state populations, while RPSH-wBA overestimated them.
• The SH-RP-iso method demonstrated satisfactory accuracy and predicted a flattening of the rate vs. driving force dependence in the Marcus inverted regime at low temperatures.
• Observed experimental trends were reproduced by the SH-RP-iso method.

Conclusions:

• The combination of FOB-SH with the SH-RP-iso method is a promising approach for accurately simulating charge transport in molecular materials and biological systems.
• This method effectively includes zero-point motion and tunneling, crucial for understanding low-temperature electronic processes.