Anhamonic finite temperature effects on the Raman and Infrared spectra to determine the crystal structure phase III of solid molecular hydrogen

We present theoretical calculations of the Raman and IR spectra, as well as electronic properties at zero and finite temperature to elucidate the crystal structure of phase III of solid molecular hydrogen. We find that anharmonic finite temperature are particularly important and qualitatively influences the main conclusions. While P6${}_3$/m is the most likely candidate for phase III at the nuclear ground state, at finite temperature the C2/c structure appears to be more suitable.