A reduced-geometry independent particle model calculation of high harmonic generation from closed-shell diatomic molecules

Abstract

We propose a simple model to calculate high harmonic spectra from closed-shell diatomic molecules based on the time-dependent Schrödinger equation. Quasi-Coulomb potentials are used to represent the two-center geometry of a diatomic molecule in two dimensions. A few outer occupied molecular orbitals are evolved independently using a single-electron Hamiltonian, and the harmonic spectra are evaluated from a coherent sum of single-electron dipole accelerations. According to this independent particle model, harmonic spectra from individual orbitals follow the semiclassical cutoff law, but their relative strengths vary depending on molecular orientations. When the contributions from different orbitals are of comparable strength, their net spectrum extends to the inner-orbital cutoffs, and in some cases acquires a local minimum where harmonic spectra from different molecular orbitals interfere destructively because of their phase difference.