Quantitative comparison of TDDFT-calculated HHG yields in ring-shaped organic molecules

TL;DR

This study uses TDDFT to compare HHG yields in three organic ring molecules, revealing overestimations in cyclohexane and proposing a correction method that improves agreement with experimental data, supporting TDDFT's utility.

Contribution

It introduces an orbital-resolved scaling correction in TDDFT calculations to improve HHG yield predictions in large molecules.

Findings

TDDFT overestimates HHG yield in cyclohexane

Orbital-resolved scaling improves comparison with experiments

TDDFT shows promise for systematic HHG computations in large molecules

Abstract

We compare the high-harmonic-generation (HHG) yield driven by a mid-infrared laser 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 in order 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 (CHA) is strongly overestimated compared to those of benzene and cyclohexene, and that this can be attributed to unphysically large contributions from CHA orbitals lying well below the highest-occupied molecular orbital. We show that implementing a simple orbital-resolved scaling factor, which corrects the yield of the tunneling ionization contribution to the first step in the HHG process, leads to much better comparisons with experimental results. Our results are encouraging for the use of TDDFT in systematic computations of HHG in large molecules.