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Area of Science:

  • Quantum chemistry
  • Computational physics
  • Molecular dynamics

Background:

  • Fewest-switches surface hopping (FSSH) is a key method for simulating molecular quantum dynamics.
  • The standard FSSH formulation is limited to adiabatic dynamics, hindering its use for coherent phenomena.
  • Constructing a complete density matrix from FSSH trajectories for coherent dynamics is an open challenge.

Purpose of the Study:

  • To investigate the construction of density matrices from FSSH trajectories for coherent quantum dynamics.
  • To identify potential issues with standard FSSH approaches when applied to coherent phenomena.
  • To evaluate a recently proposed coherent generalization of FSSH.

Main Methods:

  • Analysis of density matrix construction from FSSH trajectories.
  • Demonstration of positivity violation in standard FSSH treatments.
  • Evaluation of a coherent FSSH generalization using established metrics.

Main Results:

  • Standard FSSH methods, when defining adiabatic coherences from wavefunction coefficients, can lead to density matrix positivity violations.
  • A recently proposed coherent generalization of FSSH resolves these positivity issues.
  • The coherent FSSH approach demonstrates improved accuracy across a significant portion of the parameter space.

Conclusions:

  • The standard FSSH approach is insufficient for accurately modeling coherent quantum dynamics due to potential positivity violations.
  • Coherent generalizations of FSSH offer a more robust framework for quantum dynamics simulations.
  • The improved accuracy and guaranteed positivity of coherent FSSH make it a promising method for future research.