The Role of Multi-Electron and Multi-Orbital Effects in High-Order Harmonic Generation of Benzonitrile Molecules

Multi-electron and multi-orbital effects play a crucial role in the interaction of strong laser fields with complex molecules. Here, multi-electron effects encompass not only electron-electron Coulomb interactions and exchange-correlation effects but also the interference between the dynamics of different electron wave packets. In this study, we employ time-dependent density functional theory to investigate high-harmonic generation in benzonitrile (C₇H₅N) subjected to intense infrared laser fields. We find that when the laser polarization direction forms a 45-degree angle with the N-C-C-C axis, the HHG signal perpendicular to this axis exhibits a significant enhancement in the 23rd to 31st harmonic orders. Our analysis shows that this enhancement does not align with the classical three-step model but instead arises purely from quantum interference between different orbital channels. Our study reveals that multiple inner-shell orbitals and multi-electron effects play a crucial role in shaping this harmonic spectrum. These findings provide deeper insights into HHG mechanisms and contribute to advancements in strong-field physics and attosecond science.