Results presented here are based on a completely new implementation of the TDKS module in Q-Chem v. 5.4, 63 replacing the original TDKS code written by Nguyen et al.. In the new module, time propagation can be accomplished either based on the modifiedmidpoint algorithm, which is used here, or else selfconsistent predictor-corrector algorithms. Since the HHG process involves ionization and electron recombination, the asymptotic behavior of the exchangecorrelation function is crucial. We use an LRC variant of a range-separated hybrid functional, specifically, the LRC-ωPBE functional with range-separation parameter ω = 0.3 bohr -1 . LRC functionals, as a subset of range-separated hybrid functionals, are characterized by an asymptotic exchange functional that becomes 100% Hartree-Fock (HF) exchange for r 12 1/ω. This ensures that the asymptotic behavior of the exchange potential is -1/r. Not all range-separated hybrid functionals enforce the correct asymptotic behavior; see Ref. 39 for a discussion. To assess the role of electron correlation, we will also carry out some simulations at the level of TDHF theory, which is equivalent to TDKS with a functional that contains only HF exchange, with no correlation and no range separation.