Ab initio two-spinor Ehrenfest dynamics with magnetic field

Area of Science:

• Quantum Chemistry
• Molecular Dynamics
• Photochemistry

Background:

• The impact of external magnetic fields on excited-state molecular dynamics is poorly understood.
• This knowledge gap limits control over photochemical and photophysical processes.

Purpose of the Study:

• Develop a computational framework to simulate magnetic field effects on molecular dynamics.
• Investigate the influence of magnetic fields on excited-state processes.

Main Methods:

• Developed a finite-magnetic-field *ab initio* nonadiabatic molecular dynamics framework.
• Utilized Ehrenfest dynamics and gauge-including atomic orbitals.
• Derived analytical energy gradients in magnetic fields using a two-spinor formalism.

Main Results:

• Simulated internal rotation of methyliminium cation (CH₂NH₂⁺) and H₂ dissociation under magnetic fields.
• Identified magnetic-field-induced orbital Zeeman effect as the primary driver for CH₂NH₂⁺ isomerization.
• Observed spin-coherence generation and Larmor precession in H₂ dissociation.

Conclusions:

• Established a general framework for simulating magnetic-field-controlled nonadiabatic dynamics.
• Provided insights into manipulating photochemical and spin-dependent processes using external magnetic fields.