Nonadiabatic Coupling in Trajectory Surface Hopping: How Approximations Impact Excited-State Reaction Dynamics

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Photochemistry

Background:

• Trajectory Surface Hopping (TSH) is a widely used method for modeling photochemical reactions.
• TSH approximates quantum dynamics using mixed quantum-classical methods and ensembles of trajectories.
• Nonadiabatic effects are crucial and typically modeled using nonadiabatic coupling between electronic states.

Purpose of the Study:

• To benchmark the impact of approximations to the nonadiabatic coupling term on TSH dynamics.
• To evaluate the accuracy and efficiency of different coupling schemes for isomerization and ring-opening reactions.

Main Methods:

• Benchmarking various approximations for nonadiabatic coupling calculations.
• Utilizing the trajectory surface hopping (TSH) method.
• Implementing a biorthonormal wave function overlap scheme in OpenMOLCAS.

Main Results:

• Two schemes, local diabatization and biorthonormal wave function overlap, accurately reproduce TSH dynamics at reduced computational cost.
• A scheme based on configuration interaction vectors shows unpredictable failures.
• The Baeck-An approximation systematically overestimates hopping to the ground state.

Conclusions:

• The choice of nonadiabatic coupling approximation significantly impacts TSH dynamics accuracy.
• Local diabatization and biorthonormal overlap schemes offer efficient and accurate alternatives for TSH calculations.
• Careful selection of coupling schemes is essential to avoid erroneous simulation of photochemical reaction dynamics.