Modeling of High-Harmonic Generation in the C₆₀ Fullerene Using Ab Initio, DFT-Based, and Semiempirical Methods.

Area of Science:

• Quantum Chemistry
• Molecular Physics
• Spectroscopy

Background:

• High-harmonic generation (HHG) is a key process in strong-field physics.
• Understanding HHG in molecules like C60 requires accurate theoretical descriptions.
• Computational methods are crucial for interpreting experimental HHG spectra.

Purpose of the Study:

• To calculate and analyze the high-harmonic generation spectra of the C60 fullerene molecule.
• To investigate the influence of electron correlation and exchange effects on HHG spectra.
• To evaluate the applicability of different real-time time-dependent quantum chemical methods.

Main Methods:

• Real-time time-dependent quantum chemical methods were employed.
• Wave function propagation involved ground and singly excited eigenstates from linear-response calculations.
• Comparisons were made between Hartree-Fock, density functional theory (DFT) with various functionals, random-phase approximation (RPA), configuration interaction singles (CIS), and Tamm-Dancoff approximation (TDA).
• The semiempirical INDO/S method was extended to real-time dynamics.

Main Results:

• Distinct contributions of correlation and exchange effects to the HHG spectra were identified.
• DFT, RPA, CIS, and TDA methods showed varying degrees of agreement with theoretical predictions.
• The real-time INDO/S method demonstrated potential for approximate simulations of laser-driven dynamics in large molecular systems.

Conclusions:

• The choice of quantum chemical method significantly impacts the accuracy of calculated HHG spectra.
• Real-time TD-DFT and related methods provide valuable insights into electron dynamics during HHG.
• The INDO/S method offers a computationally feasible approach for studying large systems in strong laser fields.