Abstract
We study the gap closure with pressure of crystalline molecular hydrogen. The gaps are obtained from grand-canonical quantum MonteCarlo methods properly extended to quantum and thermal crystals, simulated by coupled electron ion MonteCarlo methods. Nuclear zero point effects cause a large reduction in the gap (∼2 eV). Depending on the structure, the fundamental indirect gap closes between 380 and 530GPa for ideal crystals and 330-380GPa for quantum crystals. Beyond this pressure the system enters into a bad metal phase where the density of states at the Fermi level increases with pressure up to ∼450-500 GPa when the direct gap closes. Our work partially supports the interpretation of recent experiments in high pressure hydrogen.
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