Coupled- and Independent-Trajectory Approaches Based on the Exact Factorization Using the PyUNIxMD Package

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• The exact factorization framework offers a rigorous approach to quantum dynamics.
• Understanding electron-nuclear correlations is crucial for describing nonadiabatic processes.

Purpose of the Study:

• To present and evaluate mixed quantum-classical methods based on the exact factorization framework.
• To investigate the role of electron-nuclear correlation in quantum coherences and nonadiabatic couplings.
• To compare coupled- and independent-trajectory approximations for molecular dynamics.

Main Methods:

• Mixed quantum-classical approaches derived from the exact factorization framework.
• Classical nuclei approximation incorporating electronic and nuclear nonadiabatic couplings.
• Comparison of coupled- and independent-trajectory algorithms.
• Excited State Molecular Dynamics (ESMD) simulations using the PyUNIxMD program.

Main Results:

• The electron-nuclear correlation term effectively manages quantum coherences.
• Coupled- and independent-trajectory approximations show distinct behaviors in nuclear wave packet bifurcation.
• Accurate spatial distribution of electronic wave functions along nuclear trajectories is achieved.
• Numerical comparisons highlight differences between the trajectory approaches for photoisomerization.

Conclusions:

• Mixed quantum-classical methods based on exact factorization provide a robust tool for simulating quantum dynamics.
• The electron-nuclear correlation term is essential for accurately capturing nonadiabatic effects.
• The choice of trajectory approximation impacts the description of nuclear dynamics and electronic state evolution.
• The PyUNIxMD program facilitates efficient ESMD simulations for complex chemical systems.