Molecular high-harmonic generation under the influence of a significant dipole moment

Using time-dependent density-functional theory, we investigate how a large permanent dipole moment modifies high-harmonic generation (HHG). Using LiH as an example, by systematically comparing spectra obtained with laser polarization parallel and perpendicular to the molecular axis, we identify distinctive features arising from pronounced Stark shifts induced by the dipole. In the parallel orientation, these shifts broaden resonance conditions and strongly enhance below-threshold harmonics, producing a plateaulike structure. A pronounced two-center interference minimum also appears near the maximum transient ionization potential. Furthermore, the variation of Stark shifts within each half optical cycle (HOC), together with their alternating signs between consecutive HOCs, introduces asymmetries in tunneling, propagation, and recombination. These asymmetries drive interference that manifests as spectral splits and blueshifts in the plateau and near-cutoff regions of the HHG spectrum.