FIG. : HHG spectra for H2 computed using the TDKS approach with two different functionals and no CAP, using the 5-aug-cc-pVTZ basis set in both cases. An impulsive field is applied, with parameters as in Fig. , and the simulations are propagated for 1,500 a.u. in time. The vertical axis shows the signal |dA(ω)| 2 on a logarithmic scale. The horizontal axis is the harmonic order, in multiples of the fundamental frequency ω 0 = 1.55 eV = 800 nm. -ε HOMO ), and depending on whether the level of theory is HF or LRC-ωPBE. (The 5-aug-cc-pVTZ basis set is used in each case.) Using the most recent estimate of the cutoff energy, 53 namely, Eq. ( ) with c 1 = 3. excitations into unbound MOs afford ionization channels.