Electronic excitation spectra of molecular hydrogen in phase I from quantum Monte Carlo and many-body perturbation methods

The electronic excitations in solid molecular hydrogen at room temperature for pressures varying from 5 to 90 GPa are calculated using quantum Monte Carlo methods and many-body perturbation theory. A crossover from a wide-gap insulator to a semiconductor is observed, showing the changing nature of the excitations from localized molecular (left inset figure) to delocalized (right inset figure) excitations. These findings are in agreement with experimental results, demonstrating the capability of accurately predicting band gaps in many-body systems with strong zero point and thermal effects.