The ab initio molecular dynamics (AIMD) method provides a computational route for the real-time simulation of reactive chemistry and spectroscopy. An often-overlooked capability of this approach is the opportunity to examine the electronic evolution of a chemical system, including chemical bond formation and electrical responses to radiation.
For AIMD trajectories based on Hartree-Fock or density functional theory (DFT) methods, the real-time evolution of orbitals can provide detailed insights into the time-dependent electronic structure of a complex. However, the molecular orbital character, ordering, and associated phase are not preserved throughout the trajectory, due to the presence of different electronic Hamiltonians at each time step. By exploiting the similarity in neighboring timesteps’ electronic structure, an algorithm has been developed that allows for reliably tracking the character of molecular orbitals throughout an AIMD trajectory, including cases of orbital crossing and degeneracy.
In this presentation, examples of the results of this tool will be shown, including reactive trajectories. These examples will also highlight the adiabatic character of the evolution of molecular orbitals. The utility of this approach for both educational purposes and analysis of trajectories will be demonstrated. Possibilities for extension to diabatic analyses will also be discussed.