Multi-state harmonic models with globally shared bath for nonadiabatic dynamics in the condensed phase.

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Materials Science

Background:

• Model Hamiltonians are essential for simulating nonadiabatic dynamics in condensed phases.
• Existing methods, like the two-state spin-boson model, are limited for systems with more than two electronic states.
• A general strategy for constructing multi-state harmonic (MSH) models is lacking due to interdependent energy gaps.

Purpose of the Study:

• To extend the approach for building three-state harmonic models to an arbitrary number of electronic states.
• To develop a general and flexible framework for simulating nonadiabatic dynamics in complex molecular systems.
• To demonstrate the MSH model construction for a specific organic photovoltaic system.

Main Methods:

• Extension of a previously proposed approach for three-state harmonic models to arbitrary numbers of states.
• Global bath and scaled system-bath couplings based on reorganization energies.
• Application to a carotenoid-porphyrin-C60 molecular triad in tetrahydrofuran solvent.
• Simulation of nonadiabatic dynamics using mixed quantum-classical techniques (linearized semiclassical, symmetrical quasiclassical, mean-field Ehrenfest, mixed quantum-classical Liouville).

Main Results:

• Successful construction of MSH models for two-, three-, and four-state systems.
• Demonstration of MSH model applicability to a complex organic photovoltaic molecular triad.
• Validation of the MSH models' capability in simulating nonadiabatic dynamics.

Conclusions:

• The MSH models offer a general and flexible framework for simulating nonadiabatic dynamics in complex systems.
• This approach overcomes limitations of previous models for multi-state systems.
• The developed method is applicable to systems relevant to organic photovoltaics and charge transfer processes.