Real-Time Time-Dependent Nuclear-Electronic Orbital Approach: Dynamics beyond the Born-Oppenheimer Approximation

Area of Science:

• Quantum mechanics
• Chemical physics
• Computational chemistry

Background:

• Nonadiabatic dynamical processes, such as proton-coupled electron transfer, require quantum mechanical treatment of both electrons and nuclei.
• The nuclear-electronic orbital (NEO) method accounts for nuclear quantum effects beyond the Born-Oppenheimer approximation.

Purpose of the Study:

• To develop and implement a real-time NEO (RT-NEO) approach for studying nonadiabatic quantum dynamics.
• To enable the investigation of nonequilibrium properties in quantum systems.

Main Methods:

• Derivation and implementation of the RT-NEO approach using time-dependent Hartree-Fock or density functional theory.
• Propagation of electronic and nuclear degrees of freedom within a time-dependent variational framework.
• Computation of the time-dependent dipole moment to resolve spectral features.

Main Results:

• Demonstrated the dynamical interplay between quantum nuclei and electrons via vibronic coupling.
• Showcased vibrational excitation using a resonant driving field.
• Illustrated electronic excitation by simulating excited-state intramolecular proton transfer.

Conclusions:

• The RT-NEO approach is a powerful tool for studying nonadiabatic quantum dynamics.
• This method provides a time-dependent variational description for coupled electronic and nuclear degrees of freedom.