Geometric Phase Effects in Nonadiabatic Dynamics near Conical Intersections.

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• The Born-Oppenheimer approximation (BOA) breaks down when electronic potential energy surfaces have small or vanishing energy differences.
• Conical intersections (CIs) are key scenarios where BOA fails, enabling efficient radiationless electronic transitions and introducing geometric phases (GPs).

Purpose of the Study:

• To investigate the impact of geometric phases (GPs) on nonadiabatic molecular dynamics.
• To explore how GPs modify dynamics initiated from ground and excited electronic states.
• To assess the importance of GPs in real molecular systems.

Main Methods:

• Utilized a simplified two-dimensional, two-state linear vibronic coupling model to study CI topology and GP effects.
• Analyzed dynamics under various initial conditions.
• Evaluated the performance of quantum and quantum-classical methods (wave packet dynamics, surface-hopping, Ehrenfest, quantum-classical Liouville equation) in capturing GP effects.

Main Results:

• Demonstrated that GPs significantly alter nonadiabatic dynamics, with their importance depending on potential energy surface topography.
• Identified specific molecular systems where GP effects are critical for accurate dynamics.
• Found that approximate methods succeed when they avoid direct action of the nuclear kinetic energy operator on electronic wave functions.

Conclusions:

• Geometric phases are essential for accurately describing nonadiabatic dynamics beyond the Born-Oppenheimer approximation.
• The influence of GPs on nuclear dynamics is highly sensitive to the shape of potential energy surfaces.
• Developing approximate methods that properly account for GPs is crucial for advancing the simulation of complex molecular systems.