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Choosing the right velocity adjustment direction in surface hopping dynamics is key. For complex molecules like protonated Schiff base (PSB4), momentum direction with a reduced kinetic energy reservoir is effective, preventing artificial back-hopping.

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Area of Science:

  • Chemical Physics
  • Computational Chemistry
  • Quantum Dynamics

Background:

  • Surface hopping dynamics are crucial for simulating non-adiabatic processes in chemical reactions.
  • Accurate simulations require careful handling of velocity adjustments during hopping events to avoid artificial dynamics.

Purpose of the Study:

  • To investigate the impact of different velocity adjustment directions on surface hopping dynamics.
  • To evaluate the effectiveness of various algorithms, including momentum and gradient-based methods, for simulating population decay and reaction yields.
  • To assess the role of the kinetic energy reservoir in preventing artificial back-hopping.

Main Methods:

  • Simulations of surface hopping dynamics using fulvene and protonated Schiff base (PSB4) as model systems.
  • Comparison of velocity adjustments in nonadiabatic coupling, gradient difference, and momentum directions.
  • Evaluation of a reduced kinetic energy reservoir approach and approximate nonadiabatic coupling vectors.

Main Results:

  • The choice of velocity adjustment direction significantly impacts results for fulvene but not for PSB4, correlating with conical intersection topography.
  • When nonadiabatic coupling vectors are unavailable, the gradient difference direction is optimal.
  • A reduced kinetic energy reservoir or momentum direction offers a viable alternative when gradient difference is unavailable, preventing excessive back-hopping.

Conclusions:

  • The kinetic energy reservoir size is more critical than the precise velocity adjustment direction for accurate non-adiabatic dynamics.
  • The gradient difference and momentum directions with a reduced kinetic energy reservoir are robust options for velocity adjustment in surface hopping.
  • Understanding conical intersection topography is essential for selecting appropriate velocity adjustment strategies.