Approximation Schemes to Include Nuclear Motion in Laser-Driven Ab Initio Electron Dynamics: Application to High...

Area of Science:

• Quantum Chemistry
• Theoretical Attochemistry
• Molecular Dynamics

Background:

• Simulating many-electron dynamics in molecules under short laser pulses is crucial for theoretical attochemistry.
• Including quantum nuclear motion is computationally intensive, often leading to the fixed-nuclear approximation in calculations.
• Previous studies on H2+ showed nuclear motion significantly impacts high harmonic generation (HHG) spectra.

Purpose of the Study:

• To develop a computationally feasible method for including quantum nuclear motion in complex molecular systems.
• To extend the treatment of coupled nuclear-electron dynamics beyond simple systems like H2+.
• To enable accurate simulations of ultrafast electron dynamics and HHG in molecules with multiple electrons and nuclei.

Main Methods:

• Approximation of Born-Oppenheimer potential energy surfaces using model potentials (harmonic and asymptotic expansions).
• Derivation of model potentials from a minimal set of ab initio calculations.
• Application of time-dependent configuration interaction (TD-CIS) for electronic structure calculations.

Main Results:

• Successful validation of the method for HHG in H2+ using few-cycle laser pulses, matching exact calculations.
• Application to diatomic molecules with multiple electrons, demonstrating broader applicability.
• Extension to a 2D model of the water molecule, showcasing its potential for more complex systems.

Conclusions:

• The proposed scheme effectively incorporates quantum nuclear motion into attochemistry simulations for complex molecules.
• Model potentials derived from ab initio data offer a computationally efficient way to handle nuclear dynamics.
• This method paves the way for more accurate theoretical studies of light-driven molecular processes.