Adiabatic Molecular Orbital Tracking in Ab Initio Molecular Dynamics

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Dynamics

Background:

• Ab initio molecular dynamics (AIMD) simulates reactive chemistry in real-time.
• Tracking molecular orbital (MO) evolution during AIMD is challenging due to changing electronic Hamiltonians.
• Understanding time-dependent electronic structure is crucial for reactive chemistry.

Purpose of the Study:

• To develop and assess an algorithm for tracking MO character, ordering, and phase during AIMD.
• To address challenges in visualizing electronic structure evolution in dynamic chemical systems.
• To provide deeper insights into the electronic mechanisms of chemical reactions.

Main Methods:

• Exploiting similarity projections of electronic structure between neighboring AIMD steps.
• Employing a quadrupole-field perturbation to resolve orbital degeneracies while conserving energy.
• Analyzing the adiabatic evolution of molecular orbitals.

Main Results:

• The algorithm successfully tracks MOs throughout AIMD trajectories, even with orbital degeneracies.
• Orbital evolution is shown to be adiabatic, clarifying electronic structure changes.
• The method provides clear interpretations of electronic structure during reactions like nucleophilic substitution.

Conclusions:

• The developed algorithm enhances the analysis of electronic structure in AIMD simulations.
• It offers a robust method for visualizing and understanding MO dynamics in reactive systems.
• This approach can clarify textbook interpretations of chemical reaction mechanisms.