Core-polarization effects in molecular high harmonic generation

By comparing three-dimensional multi-electron calculations with several simplifying models, we show that polarization of the molecular ion can crucially contribute to the high harmonic spectra of molecules. We solve the time-dependent Schrodinger equation for diatomic model molecules with up to 4 active electrons using the multi-configuration time-dependent Hartree-Fock method. Single electron models fail to reproduce the harmonic spectra as they do not account for polarization of the multi-electron ionic core by the laser field. We find the dominant mechanism in the modification of the recombination dipole matrix element, while ionization is only mildly affected.