Parameter-free ionization model for atomic and molecular high-harmonic generation spectra using Gaussian basis sets.

Area of Science:

• Quantum dynamics
• Attosecond science
• Computational chemistry

Background:

• High-Harmonic Generation (HHG) is vital for studying ultrafast electron dynamics.
• Gaussian basis sets are used with wave function methods for HHG calculations.
• Basis set incompleteness and ionization are critical for accurate HHG spectra.

Purpose of the Study:

• To comparatively analyze the ab initio lifetime model (AbILM) and heuristic lifetime models (HLMs).
• To assess the impact of basis set incompleteness treatments on HHG spectra.
• To evaluate the reliability and potential biases of different lifetime correction approaches.

Main Methods:

• Comparative analysis of AbILM and HLMs.
• Calculations using time-dependent configuration interaction singles (TD-CIS) and doubles (TD-CISD).
• Focus on hydrogen and helium atoms, hydrogen and nitrogen molecules.

Main Results:

• Different treatments of basis set incompleteness significantly influence HHG spectra accuracy.
• The study quantifies the impact of lifetime correction models on ionization and spectral features.
• AbILM and HLMs show varying degrees of reliability for different systems.

Conclusions:

• Accurate treatment of basis set incompleteness is crucial for reliable HHG predictions.
• The choice of lifetime model can introduce biases in HHG spectra.
• This work provides insights for selecting appropriate methods in attosecond science.