title: Dissociation of high-pressure solid molecular hydrogen: a quantum Monte Carlo and anharmonic vibrational study.
abstract: A theoretical study is reported of the molecular-to-atomic transition in solid hydrogen at high pressure. We use the diffusion quantum Monte Carlo method to calculate the static lattice energies of the competing phases and a density-functional-theory-based vibrational self-consistent field method to calculate anharmonic vibrational properties. We find a small but significant contribution to the vibrational energy from anharmonicity. A transition from the molecular Cmca-12 direct to the atomic I41/amd phase is found at 374 GPa. The vibrational contribution lowers the transition pressure by 91 GPa. The dissociation pressure is not very sensitive to the isotopic composition. Our results suggest that quantum melting occurs at finite temperature.
authors.affiliation: Thomas Young Centre and Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Sam
authors.initials: S
authors.lastname: Azadi
authors.affiliation: TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Bartomeu
authors.initials: B
authors.lastname: Monserrat
authors.affiliation: Thomas Young Centre and Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: W M C
authors.initials: WM
authors.lastname: Foulkes
authors.affiliation: TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: R J
authors.initials: RJ
authors.lastname: Needs