Description
High-harmonic generation (HHG) is a central process in attosecond science and an emerging tool for probing ultrafast electron dynamics in molecules. Its theoretical description is particularly demanding, as it requires the simultaneous treatment of continuum dynamics, ionization, and many-electron effects.
In this seminar, I will present a theoretical approach in the field of quantum chemistry developed for the study of HHG in atomic and molecular systems. A first challenge concerns the representation of electronic continuum states within Gaussian basis sets commonly used in quantum chemistry. I will discuss how tailored basis functions can provide an accurate description of harmonic emission, and how basis-set incompleteness can be addressed through parameter-free lifetime corrections that effectively account for ionization processes without empirical parameters [1,2].
I will then turn to the role of electron correlation in strong-field dynamics, showing how correlated wave-function methods can significantly affect harmonic intensities, spectral structures, and the description of multielectron effects beyond single-active-electron pictures [3]. Finally, I will present time-dependent molecular-orbital decomposition techniques, which offer direct insight into the orbital channels contributing to HHG and reveal interference effects that encode molecular electronic structure in the emitted spectrum [4].
References
[1] C. Morassut, E. Coccia, E. Luppi, Quantitative performance analysis and comparison of optimal-continuum Gaussian basis sets for high-harmonic generation spectra, J. Chem. Phys. 159, 124108 (2023).
[2] P. A. Albrecht, C. Morassut, E. Coccia, T. Klamroth, P. Saalfrank, E. Luppi, Parameter-free ionization model for atomic and molecular high-harmonic generation spectra using Gaussian basis sets, J. Chem. Phys. 163, 024135 (2025).
[3] C. F. Pauletti, E. Coccia, E. Luppi, Role of exchange and correlation in high-harmonic generation spectra of H2, N2, and CO2 : Real-time time-dependent electronic-structure approaches, J. Chem. Phys. 154, 014101 (2021).
[4] M. Marchetta, C. Morassut, J. Toulouse, E. Coccia, E. Luppi, Time-dependent ab initio molecular-orbital decomposition of high-harmonic generation spectra, J. Chem. Phys. 161, 204111 (2024).
