Photoexcited Charge Transfer Reactions | Method Development and Materials Simulation Lab

Photoinduced Proton-coupled electron transfer reactions

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Photoinduced proton-coupled electron transfer (PI-PCET), is at the heart of energy conversion reactions in photosynthesis and respiration.Understanding the underlying mechanistic principles of PI-PCET will allow us to tune and control this reaction and use this knowledge to design novel solar energy conversion devices. To accomplish this goal, we develop theoretical approaches that account for non-adiabatic transitions during ET processes, and non-equilibrium configuration of solvent upon photoexcitation.

Mixed Quantum-Classical Liouville

MQCL is a surface-hopping algorithm based on the numerical solution of the quantum-classical Liouville equation where proton and electron are treated quantum mechanically while the environmental degrees of freedom are accounted for classically. In MQCL, the classical degrees of freedom are evolved either on single adiabatic surfaces or on the mean of two surfaces as opposed to just on single adiabatic surfaces as in conventional fewest-switches surface hopping methods. Therefore, MQCL inherently and rigorously accounts for quantum coherence/decoherence effects in PI-PCET.

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Shakib, F.A.; Hanna, G. “Mixed Quantum-Classical Liouville Approach for Calculating Proton-Coupled Electron-Transfer Rate Constants”, J. Chem. Theory Comput., 2016, 12, 3020–3029.

Shakib, F.A.; Hanna, G. “New Insight into the Nonadiabatic State Population Dynamics of Model Proton-Coupled Electron Transfer Reactions from the Mixed Quantum-Classical Liouville Approach”, J. Chem. Phys. 2016, 144, 024110.

Shakib, F.A.; Hanna, G. “An Analysis of Model Proton-Electron Transfer Reactions via the Mixed Quantum-Classical Liouville Approach”, J. Chem. Phys. 2014, 141, 044122.

Ring polymer surface-hopping

RPSH is one of the potentially promising methods for simulating nonadiabatic dynamics of PI-PCET. In RPSH method, the nonadiabatic electronic transitions are described by the surface-hopping algorithm, and the nuclear quantum effects are incorporated through ring polymer quantization, thus making RPSH a well-tailored theoretical tool for describing the electronic and nuclear quantum dynamics. Investigating Tully’s Model systems, we demonstrated that RPSH can properly describe tunneling, nuclear ZPE, and decoherence. As such, we are developing new approximated quantum dynamics methods that are capable of accounting for both electronic nonadiabatic transitions and nuclear quantum effects, just like RPSH.

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Shakib, F.A.*; Huo, P. “Ring Polymer Surface Hopping: Incorporating Nuclear Quantum Effects into Nonadiabatic Molecular Dynamics Simulations”, J. Phys. Chem. Lett. 2017, 8, 3073–3080.

Quasi-diabatic scheme

To bridge the gap between accurate diabatic dynamics approaches and adiabatic electronic structure methods, we have developed the quasi-diabatic (QD) propagation scheme. This scheme uses the adiabatic states associated with a reference geometry as the local diabatic states during a short-time propagation step and dynamically updates the definition of the diabatic states along the time-dependent nuclear trajectory. It allows a seamless interface between diabatic dynamics approaches with commercially available adiabatic electronic structure methods to study the challenging PI-PCET reactions in realistic systems.

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Mandal, A.; Sandoval J.S.; Shakib, F.A.*; Huo, P. “Direct Simulation of Proton-Coupled Electron Transfer Reaction with Quasi Diabatic Propagation Scheme”, J. Phys. Chem. A, 2019, 123, 2470.

Mandal, A.; Shakib, F.A.; Huo, P. “Investigating Photoinduced Proton Coupled Electron Transfer Reaction using Quasi Diabatic Dynamics Propagation”, J. Chem. Phys. 2018, 148, 244102.