Origin of symmetry-forbidden high-order harmonic generation in the time-dependent Kohn-Sham formulation

Xiaoning Zang, Ce Shang, Pengcheng Zhang, Yalei Zhu, Zhiyong Zhu, Udo Schwingenschlögl

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We find, for two-electron closed-shell systems (H2 molecule, He atom), symmetry-forbidden peaks in the high-order harmonic spectra obtained by the time-dependent Kohn-Sham equations, and clarify their origin. It turns out that fixation of the number of Kohn-Sham orbitals and their occupations gives rise to unphysical transition paths and, therefore, incorrect populations of the one-electron excited states, which leads to even-order harmonics in systems with inversion symmetry. We show that the time-dependent natural Kohn-Sham and time-dependent configuration interaction equations do not suffer from this shortcoming.
Original languageEnglish (US)
JournalPhysical Review A
Issue number4
StatePublished - Apr 12 2021

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