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Identifying the atomic structures of the different phases of molecular solid hydrogen is extremely challenging, because hydrogen atoms interact with X-rays very weakly and only small samples of solid hydrogen can be achieved in
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of these structures and hence to obtain a theoretical pressure-temperature phase diagram that is in reasonable quantitative agreement with experiment. On this basis, Phase II is believed to be a molecular structure of
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calculations have been used to search for candidate atomic structures for each phase. These candidate structures have low free energies and Raman spectra in agreement with the experimental spectra.
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At low temperatures and at pressures up to around 400 GPa (3,900,000 atm), hydrogen forms a series of solid phases formed from discrete H
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of samples. Furthermore, atomic structures can be inferred from a combination of experimental Raman spectra and first-principles modelling.
255:
I. Goncharenko & P. Loubeyre (2005). "Neutron and X-ray diffraction study of the broken symmetry phase transition in solid deuterium".
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symmetry consisting of flat layers of molecules in a distorted hexagonal arrangement; and Phase IV is (or is similar to) a structure of
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methods together with a first-principles treatment of anharmonic vibrational effects have then been used to obtain the relative
44:, 7th series, vol. 18, Oct. 1899. Solid hydrogen has a density of 0.086 g/cm making it one of the lowest-density solids.
746:
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C. J. Pickard, M. Martinez-Canales and R. J. Needs (2012). "Density functional theory study of phase IV of solid hydrogen".
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in 1899 and published with the title "Sur la solidification de l'hydrogène" (English: On the freezing of hydrogen) in the
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symmetry, consisting of alternate layers of strongly bonded molecules and weakly bonded graphene-like sheets.
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occurs at low temperatures and pressures, and consists of a hexagonal close-packed array of freely rotating H
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molecules are no longer able to rotate freely. If the pressure is further increased at low temperature, a
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N. D. Drummond, B. Monserrat, J. H. Lloyd-Williams, P. Lopez Rios, C. J. Pickard and R. J. Needs (2015).
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618:"Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures"
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C. J. Pickard & R. J. Needs (2009). "Structures at high pressure from random searching".
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of 14.01 K (−259.14 °C; −434.45 °F). It was collected for the first time by
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H.-K. Mao & R. J. Hemley (1994). "Ultrahigh-pressure transitions in solid hydrogen".
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occurs at a temperature of a few hundred kelvin at a range of pressures above 220 GPa.
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R. T. Howie, C. L. Guillaume, T. Scheler, A. F. Goncharov and E. Gregoryanz (2012).
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is encountered at about 160 GPa. Upon increasing the temperature, a transition to a
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occurs at up to 110 GPa. Phase II is a broken-symmetry structure in which the H
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molecules. Upon increasing the pressure at low temperature, a transition to
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Melting
Characteristics and Bulk Thermophysical Properties of Solid Hydrogen
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provides very limited information about the structures. Nevertheless,
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J. M. McMahon, M. A. Morales, C. Pierleoni and D. M. Ceperley (2012).
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417:"The properties of hydrogen and helium under extreme conditions"
30:, achieved by decreasing the temperature below hydrogen's
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symmetry; Phase III is (or is similar to) a structure of
372:& I. A. Troyan (2011). "Conductive dense hydrogen".
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Properties of solid hydrogen at very low temperatures
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can be detected by looking for abrupt changes in the
308:"Mixed Molecular and Atomic Phase of Dense Hydrogen"
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186:Correspondence and General A-I DEWAR/Box D I
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481:"Structure of phase III of solid hydrogen"
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16:The frozen form of the 1-proton element
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199:"Sur la solidification de l'hydrogène"
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167:Timeline of hydrogen technologies
203:Annales de Chimie et de Physique
41:Annales de Chimie et de Physique
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595:10.1103/PhysRevB.85.214114
444:10.1103/RevModPhys.84.1607
707:, Technical Report, 1972
242:10.1103/RevModPhys.66.671
102:Density functional theory
48:Molecular solid hydrogen
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747:Solid-state chemistry
522:Phys. Status Solidi B
197:Dewar, James (1899).
26:state of the element
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263:(7046): 1206–1209.
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147:Compressed hydrogen
110:Gibbs free energies
106:Quantum Monte Carlo
86:diamond anvil cells
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157:Metallic hydrogen
94:phase transitions
90:X-ray diffraction
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209:: 145–150.
173:References
88:, so that
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485:Nat. Phys
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141:See also
78:Phase IV
66:Phase II
28:hydrogen
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58:Phase I
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