Equation of State for Solid Hydrogen

Neutron diffraction determination of the microscopic structure of solid deuterium close to melting

“…Thus, in condensed matter the particle wave function becomes even more localized, eventually ending in an almost classical behavior when the density grows beyond a certain limit. 25 Nevertheless, if the pressure remains within reasonable values ͑i.e., close or below ambient pressure͒, the estimate based on DB is still a good approximation even in condensed phase, provided k B T is replaced by two-thirds of the mean kinetic energy, which plays the role of an effective temperature. Among the various reasons for the relative lack of accurate information on the microscopic structure of H 2 and D 2 solids, one may quote the experimental difficulties of performing precise x-ray diffraction ͑due to the large electron delocalization in molecular hydrogen͒, as well as neutrondiffraction experiments ͑due to the size of H incoherent scattering and to the inelastic corrections in both isotopes͒, as proved, for example, by the pioneering neutron experiments of Ishmaev et al 26 A complete review of the diffraction studies on H 2 and D 2 can be found in Ref.…”

Molecular hydrogen confined within nanoporous framework materials: Comparison of density functional and classical force-field descriptions

“…[6][7][8][9] Such potentials have been extensively used and range in complexity from simple two parameter LennardJones forms to more accurate multiparameter potential forms ͑e.g., Buck et al, Silvera-Goldman͒. 1,4,10 Many such potentials describe the weak intermolecular hydrogen interaction in a spherically symmetric manner, which is found to be an excellent approximation when the results of their usage are compared with experimental data. The accuracy of such centrosymmetric H 2 -H 2 potentials is also evidenced by their use in the setup of high level quantum mechanical calculations of H 2 cluster systems, 11,12 the calculation of the properties of bulk dense H 2 phases, 2,3 and also for larger scale classical molecular dynamics calculations.…”

“…It is also increasingly important recently, due to the application potential of efficient storage of hydrogen as a clean portable energy resource. For the purposes of studying both bulk and clusters of H 2 molecules numerous H 2 -H 2 interaction potentials have been developed through the consideration of experimental data, [1][2][3][4][5] and via high level ab initio calculations of H 2 dimers. [6][7][8][9] Such potentials have been extensively used and range in complexity from simple two parameter LennardJones forms to more accurate multiparameter potential forms ͑e.g., Buck et al, Silvera-Goldman͒.…”

The experimental heat capacity of solid hydrogen as a function of molar volume

“…If the above calculations are carried out for solid helium or solid molecular hydrogen, imaginary frequencies appear, with the difficulty lying in the assumption of small oscilla tions. For hydrogen at low temperatures and pressures, the zero point energy is about 47% of the cohesive energy (23,24) which, on extrapola tion of the calculations of Pollack e_t a^. (25), represents a motion of roughly 15-20% of the nearest neighbor distance.…”

“…Bruce (24) used the above formulation along with the 6-12 potential and calculated the expectation values using Monte Carlo techniques. His calculations were done with an fee lattice constructed out of 256 par ticles.…”