Sampling effects in quantum mechanical/molecular mechanics trajectory surface hopping non-adiabatic dynamics

Area of Science:

• * Computational Chemistry
• * Quantum Dynamics
• * Photochemistry

Background:

• * Non-adiabatic dynamics are crucial for understanding photochemical processes.
• * Hybrid quantum mechanical/molecular mechanics (QM/MM) methods are employed to study these dynamics.
• * The influence of initial conditions on simulation outcomes is often a critical factor.

Purpose of the Study:

• * To investigate the impact of various initial condition sampling methods on non-adiabatic dynamics.
• * To analyze how quantum sampling (Wigner distribution, thermal equilibration) affects excited-state relaxation.
• * To determine the influence of initial geometries and momenta on the ultrafast decay of solvated fulvene.

Main Methods:

• * Hybrid QM/MM scheme for non-adiabatic trajectory surface hopping simulations.
• * Comparison of three initial condition sampling strategies: Wigner distribution, classical molecular dynamics (thermal sampling), and quantum-sampled/thermally equilibrated systems.
• * Analysis of excited-state decay dynamics and the role of initial geometries and momenta.

Main Results:

• * Excited-state decay from the first singlet state to the ground state is highly dependent on initial conditions and simulation parameters.
• * Different sampling methods yield distinct distributions of initial geometries and momenta.
• * These variations in initial states significantly alter the excited-state dynamics and relaxation pathways of solvated fulvene.

Conclusions:

• * The choice of initial condition sampling is critical for accurately modeling non-adiabatic dynamics in QM/MM simulations.
• * Understanding these effects is essential for predicting photochemical behavior, particularly in environmentally coupled systems.
• * The study provides insights for selecting appropriate initialization strategies for future non-adiabatic dynamics simulations.