Instanton theory for Fermi's golden rule and beyond

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Theoretical Chemistry

Background:

• Instanton theory approximates quantum tunnelling in molecular systems, typically for proton transfer under the Born-Oppenheimer approximation.
• Non-adiabatic processes like electron transfer require Fermi's golden rule, not the standard Born-Oppenheimer approximation.

Purpose of the Study:

• Generalize instanton theory for non-adiabatic reactions in the Fermi's golden rule limit.
• Extend instanton theory to fourth-order processes, including bridge-mediated electron transfer.
• Apply the generalized theory to simulate electron transfer in a model quantum dot system.

Main Methods:

• Generalization of instanton theory to accommodate non-adiabatic dynamics.
• Application of the extended theory to fourth-order processes.
• Simulation of electron transfer through a three-quantum-dot model system.

Main Results:

• The generalized instanton theory successfully treats non-adiabatic reactions.
• Simulations of electron transfer in a quantum dot system show high accuracy.
• Instanton results demonstrate superior reliability compared to superexchange or classical sequential models.

Conclusions:

• The generalized instanton theory provides a powerful tool for studying non-adiabatic quantum tunnelling.
• This approach offers a more accurate alternative to existing approximations for complex electron transfer systems.
• The study advances theoretical methods for quantum processes beyond the Born-Oppenheimer approximation.