Pair potentials and equation of state of solidpara-hydrogen to megabar pressure

Abstract

We compute by means of Quantum Monte Carlo simulations the equation of state of bulk solid parahydrogen extrapolated to zero temperature, up to a pressure of ∼ 2 MBar. We compare the equation of state yielded by three different pair potentials, namely the Silvera-Goldman, Buck and one recently proposed by Moraldi, modified at short distances to include a repulsive core, missing in the originally proposed potential. The Moraldi pair potential yields an equation of state in very good agreement with experiment at megabar pressures, owing to its softer core, and is at least as accurate as the SG or the Buck at saturated vapour pressure. Estimates for the experimentally measurable kinetic energy per molecule are provided for all pair potentials. arXiv:1303.1169v4 [cond-mat.mtrl-sci]

Enhanced superfluid response of parahydrogen in nanoscale confinement

“…This is of course consistent with the greater adsorption exerted by the glass cavity, and gives us an idea of the range within which N can vary, inside a cavity of this size. An interesting thing to note is that for a Cs cavity the minimum occurs at an energy close to −88.5 K, identical to the ground state chemical potential [18] for solid p-H 2 . This means that a cavity of this size is barely at the wetting threshold for a weakly adsorbing substrate such as Cs.…”

“…For v, which we regard as spherically symmetric, we use both the well-known pair potential of Silvera and Goldman [16], as well as a recently proposed modification [17,18] thereof, which has been shown to afford an accurate reproduction of the experimental equation of state of solid p-H 2 up to megabar pressure. Computed structural and energetic properties, as well as the main conclusion regarding the superfluid response, do not depend on which potential is used.…”

Refinement of the experimental dynamic structure factor for liquid para-hydrogen and ortho-deuterium using semi-classical quantum simulation

“…26 The SG potential has been used in a number of previous studies [8][9][10][12][13][14] and has been shown to provide very accurate descriptions of the fluid and solid thermodynamics, except at extremely high pressure. 27,28 This semi-empirical isotropic pair potential, applicable to both para-hydrogen and ortho-deuterium, treats each molecule as a spherical particle which is justifiable at low temperatures since only the J = 0 rotational state is populated in each isotope. When performing the FK-LPI simulation, to expedite the determination of the FK centroid potential we represented the SG potential as a sum over four Gaussian functions whose parameters can be found in Table II of Ref. 11.…”

Computer Simulation Study of Nanoscale Size Parahydrogen Clusters

“…For example, the kinetic energy per molecule is 54.2(1) K at T =1 K, virtually unchanged, within the statistical uncertainties of the calculation, as the temperature is raised all the way to T =10 K. The energy per molecule at T =1 K is −64.5(1) K, which can be compared against that (∼ −88 K) for bulk hcp p-H 2 at the equilibrium density of 0.0261Å −3 at the same temperature (the corresponding kinetic energy per molecule is ∼ 70 K). 38 The significant difference in energy per molecule suggests that this cluster is still quantitatively far from bulk, and in particular that p-H 2 molecules experience significantly less localization than in the crystalline bulk phase. This by itself is consistent with liquidlike behavior, but of course greater insight is afforded by a direct examination of the structure of the cluster.…”