Quantitative comparison of high-order harmonic yields in ring-shaped organic molecules calculated using time-dependent density-functional theory

We compare the high-harmonic-generation (HHG) yield driven by a midinfrared laser field in three organic ring-shaped molecules, calculated using time-dependent density-functional theory (TDDFT). We average the yield over the relative orientation of the molecules and the linearly polarized, 1825-nm driving laser pulse to compare to experimental spectra obtained by Alharbi et al., [Phys. Rev. A 92, 041801 (2015)]. We find that the raw TDDFT-calculated HHG yield in cyclohexane is strongly overestimated compared to those of benzene and cyclohexene, and that this can be attributed to unphysically large contributions from cyclohexane orbitals lying well below the highest-occupied molecular orbital. We demonstrate this by implementing a simple orbital-resolved scaling factor that adjusts the tunneling-ionization contribution to the harmonic yield. The rescaled yields are in much better agreement with experimental results, and in particular, reproduce the correct relative-yield ordering of the three molecules. Our results are encouraging for the use of TDDFT in systematic computations of HHG in large molecules.