Path-integral isomorphic Hamiltonian for including nuclear quantum effects in non-adiabatic dynamics

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Chemical Dynamics

Background:

• Accurately simulating chemical dynamics requires incorporating nuclear quantum effects.
• Non-adiabatic processes, involving multiple electronic states, are particularly challenging to model.
• Existing methods often struggle with quantum effects like tunneling.

Purpose of the Study:

• To develop a path-integral approach for including nuclear quantum effects in non-adiabatic chemical dynamics.
• To introduce an isomorphic Hamiltonian for exact quantum Boltzmann distribution.
• To enable seamless integration with mixed quantum-classical dynamics methods.

Main Methods:

• Development of a general isomorphic Hamiltonian for multi-level electronic systems.
• Demonstration of reduction to Ring Polymer Molecular Dynamics (RPMD) or Centroid Molecular Dynamics (CMD) in the single-level limit.
• Combination of the isomorphic Hamiltonian with surface hopping and Ehrenfest dynamics.

Main Results:

• The isomorphic Hamiltonian correctly samples the quantum Boltzmann distribution using classical nuclear dynamics.
• Successful application to model two- and three-level systems.
• Improved simulation accuracy in the deep-tunneling regime compared to previous methods.

Conclusions:

• The isomorphic Hamiltonian provides a robust framework for incorporating nuclear quantum effects in non-adiabatic dynamics.
• This approach enhances the capabilities of mixed quantum-classical simulations.
• The method shows significant promise for accurately modeling complex chemical processes.