Accurate theoretical methods for photoionization of H$_2$ molecules
Single-photon ionization cross sections of molecular hydrogen in the electric dipole limit are numerically computed by employing three independent methods. Both time-dependent and -independent approaches within the clamped-nuclei approximation at equilibrium internuclear distance are used, featuring the explicit time-propagation of the time-dependent Schrödinger equation and newly developed multi-channel configuration-interaction free-boundary as well as complex-scaling methods using an explicitly correlated geminal basis set. The found results show convincing mutual agreement despite their entirely different fundamental formulations. They further highlight the challenges in bringing together different theoretical predictions from literature with the experimental data at high photon energies. Overall, the novel CI-based approach demonstrates fast and controllable convergence while being able to provide full channel-resolved information, indicating the need for more accurate experimental data.