Electronically nonadiabatic dynamics via semiclassical initial value methods.

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• The Meyer and Miller (MM) Hamiltonian (1979) enabled classical simulations of molecular nonadiabatic dynamics by treating nuclear and electronic degrees of freedom classically.
• Stock and Thoss (1997) demonstrated that the MM Hamiltonian is a representation, not a model, yielding exact quantum dynamics when used in the Schrödinger equation (MMST Hamiltonian).

Purpose of the Study:

• To explore the application of semiclassical (SC) initial value representations (IVRs) with the MMST Hamiltonian for describing electronically nonadiabatic processes.
• To elucidate how SC-IVR treatments using MMST trajectories capture nuclear motion in nonadiabatic regions, differing from traditional Ehrenfest models.

Main Methods:

• Utilizing the Meyer-Miller-Stock-Thoss (MMST) nuclear-electronic Hamiltonian.
• Employing semiclassical (SC) initial value representations (IVRs) with classical trajectories generated by the MMST Hamiltonian.
• Analyzing the behavior of nuclear motion in regions of nonadiabaticity.

Main Results:

• Classical trajectories generated by the MMST Hamiltonian, while technically Ehrenfest trajectories, lead to nuclear motion emerging from specific potential energy surfaces (PESs) within the SC-IVR framework.
• This behavior contrasts with the traditional Ehrenfest model, which predicts nuclear motion on an averaged PES.
• The SC-IVR approach with MMST trajectories offers a more accurate description of nonadiabatic dynamics.

Conclusions:

• The MMST Hamiltonian, when combined with SC-IVR methods, provides a powerful and unified framework for simulating complex molecular dynamics.
• This approach accurately captures the distinct behavior of nuclear motion during nonadiabatic transitions, avoiding artificial averaging over potential energy surfaces.