Semiclassical description of electronically nonadiabatic dynamics via the initial value representation.

Area of Science:

• Quantum Chemistry
• Chemical Dynamics
• Theoretical Chemistry

Background:

• Semiclassical (SC) theory and the Meyer-Miller/Stock-Thoss (MMST) description are employed to study electronically nonadiabatic processes.
• The traditional Ehrenfest model, a mixed quantum-classical approach, often fails to capture the correct correlation between electronic and nuclear dynamics.

Purpose of the Study:

• To investigate the application of the initial value representation (IVR) of SC theory combined with the MMST description for nonadiabatic processes.
• To highlight the advantages of the SC-IVR framework over the traditional Ehrenfest model in describing coupled electronic-nuclear dynamics.

Main Methods:

• Utilizing the initial value representation (IVR) of semiclassical (SC) theory in conjunction with the Meyer-Miller/Stock-Thoss description.
• Deriving and analyzing the Ehrenfest equations of motion for nuclear and electronic degrees of freedom within the SC-IVR framework.
• Performing calculations using forward-backward versions of SC-IVR theory and the linearized approximation (LSC-IVR).

Main Results:

• The SC-IVR framework yields Ehrenfest equations of motion that correctly describe the correlation between electronic and nuclear dynamics, avoiding the shortcomings of the traditional Ehrenfest model.
• Unlike the traditional Ehrenfest model, which uses an averaged potential energy surface, SC-IVR ensures nuclear motion occurs on specific potential energy surfaces corresponding to the electronic state.
• The linearized approximation (LSC-IVR) shows marginal improvement over the Ehrenfest model but fails to describe quantum coherence effects and the correct electronic-nuclear dynamics correlation.

Conclusions:

• The SC-IVR, when combined with the MMST electronic description, provides an accurate treatment of electronically nonadiabatic processes by correctly correlating nuclear and electronic dynamics.
• The SC-IVR framework offers a significant improvement over the traditional Ehrenfest model for simulating nonadiabatic dynamics, particularly in capturing quantum coherence effects.
• The linearized approximation (LSC-IVR) is insufficient for accurately describing the correlated nuclear and electronic dynamics in nonadiabatic processes due to its inability to handle quantum coherence.