The metallization of high pressure hydrogen, together with the associated molecular-to-atomic transition, is one of the most important problems in the field of high pressure physics. It is also currently a matter of intense debate due to the existence of conflicting experimental reports on the observation of metallic hydrogen on a diamond anvil cell. Theoretical calculations have typically relied on a mean-field description of electronic correlation through density functional theory, a theory

more »

... th well-known limitations in the description of metal-insulator transitions. In fact the predictions of the pressure driven dissociation of molecules in high pressure hydrogen by density functional theory is strongly affected by the chosen exchange-correlation functional. In this article we use quantum Monte Carlo calculations to study the molecular-to-atomic transition in hydrogen. We obtain a transition pressure of 447(3) GP a, in excellent agreement with the best experimental estimate of the transition, 450 GP a, based on an extrapolation to zero band gap from experimental measurements. Additionally, we find that C2/c is stable almost up to the molecular-to-atomic transition, in contrast to previous DFT and DFT+QMC studies which predict large stability regimes for intermediary molecular phases.