Quantum mechanical/molecular mechanical trajectory surface hopping molecular dynamics simulation by spin-flip...

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Physical Chemistry

Background:

• Nonadiabatic molecular dynamics simulations are crucial for understanding photochemical processes.
• Accurate modeling of excited-state dynamics in solution remains a computational challenge.
• Existing methods often struggle with describing conical intersections and transitions between electronic states.

Purpose of the Study:

• To extend spin-flip time-dependent density functional theory (SF-TDDFT) for solution-phase nonadiabatic dynamics.
• To develop a hybrid quantum mechanical/molecular mechanics (QM/MM) approach incorporating SF-TDDFT.
• To investigate the photoisomerization of E-azomethane and a green fluorescent protein chromophore in water.

Main Methods:

• Implementation of SF-TDDFT within a QM/MM framework for trajectory surface hopping simulations.
• Modification of computational code to handle electrostatic interactions between QM and MM regions.
• Extraction of classical molecular mechanics (MM) energies and forces from external program packages.

Main Results:

• The developed SF-TDDFT-QM/MM method successfully models the S₀/S₁ crossing points and S₁ → S₀ nonadiabatic transitions.
• Simulations of aqueous E-azomethane photoisomerization show good agreement with previous multireference studies.
• The method provides accurate dynamics for the anionic green fluorescent protein chromophore in aqueous solution.

Conclusions:

• SF-TDDFT, even at a single-reference level, can accurately describe nonadiabatic dynamics in condensed phases.
• The QM/MM extension of SF-TDDFT offers a computationally feasible approach for solution-phase photochemical reactions.
• This method provides a valuable tool for studying complex excited-state processes in biologically and chemically relevant environments.