Atomistic simulations of out-of-equilibrium quantum nuclear dynamics.

Area of Science:

• Condensed Matter Physics
• Quantum Dynamics
• Materials Science

Background:

• Ultrafast laser technology enables probing crystal dynamics, but interpretation is complex due to nonlinear responses.
• Quantum effects of ions become significant in light atom crystals and at low temperatures.
• Simulating nonequilibrium quantum ionic dynamics from first principles is crucial.

Purpose of the Study:

• To develop a general, first-principles method for simulating nonequilibrium quantum ionic dynamics in crystals.
• To accurately model complex nonlinear responses in laser-excited crystal systems.
• To enable simulations of advanced spectroscopic techniques like ultrafast THz-Xray pump-probe spectroscopy.

Main Methods:

• Utilized the nonequilibrium time-dependent self-consistent harmonic approximation (TD-SCHA).
• Implemented a stable, energy-conserving, correlated stochastic integration scheme for high accuracy.
• Method is compatible with first-principles electronic treatments or machine-learning potentials.

Main Results:

• Achieved high accuracy ($$) in simulating quantum ionic dynamics.
• Validated the method with a 1D model and a realistic 40-atom SrTiO₃ cell under THz laser pump.
• Demonstrated the capability to model complex crystal responses to ultrafast excitation.

Conclusions:

• The developed TD-SCHA method provides a robust tool for studying ultrafast dynamics in crystals.
• This work paves the way for simulating advanced pump-probe spectroscopy experiments.
• Enables deeper insights into quantum ionic behavior in materials under extreme conditions.