Sound velocities in solid hydrogen under pressure

Freǐman, Yu. A.; Grechnev, Alexei; Tretyak, S. M.; Goncharov, Alexander F.; Hemley, Russell J.

doi:10.1063/1.4807043

Cited by 4 publications

(4 citation statements)

References 46 publications

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“…The calculations were carried out using the DFT and semi-empirical (SE) approaches. The results for hydrogen extend our previous results 47 . The elastic properties of He under pressure were previously investigated within DFT using an atomic-based EMTO code 48 .…”

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Sound velocities of hexagonal close-packed H2and He under pressure

et al. 2013

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Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the closepacked hexagonal structure are calculated over a wide pressure range using two complementary approaches: semi-empirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in the generalized gradient approximation. The sound velocities are used to calculate pressure dependence of the Debye temperature. The comparison between experiment and first-principle and semi-empirical calculations provide constraints on the density dependence of intermolecular interactions in the zero-temperature limit. 62.20.dj Hydrogen and helium are the simplest and most abundant chemical elements in the Universe. Studies of solid helium and hydrogen at elevated pressures, which started at the end of the 1920s, are of great interest for many branches of science. Hydrogen and helium are major constituents of stars and giant planets and their physical properties are very important for condensed matter physics, planetary science and astrophysics. As such the behavior of these elements under extreme environments of pressure and temperature is central to modeling the interiors of planetary and astrophysical bodies.High-pressure x-ray, Raman and infra-red (IR) studies established three molecular phases of solid hydrogen 1-4 . These phases are related to the orientational ordering of the molecules and structural transitions. In phase I, which is stable at zero temperature up to 110 GPa, hydrogen molecules are quantum rotors arranged in the hexagonal-close-packed (hcp) structure. At the I -II phase transition the molecules go from the quantum rotor state to a strongly anharmonic anisotropic librational state. Above 150 GPa solid hydrogen transforms to phase III. The molecular ordering in this phase can be treated classically. Thus, for this part of the phase diagram the most general picture can be formulated in terms of the concept of quantum versus classical orientational ordering 5 . Although the structures of phases II and III are unknown, x-ray and Raman data suggest that the hydrogen molecules in both phases lie close to the sites of the hcp lattice 6,7 . At low temperatures the molecules are stable to at least 360 GPa; but hydrogen transforms to new phases (e.g., phase IV) with increasing temperature at these pressures [8][9][10][11] .At low pressures and temperatures 4 He crystallizes into the hcp structure. High-pressure x-ray diffraction measurements 12-14 have shown that in a wide temperature (up to 400 K) and pressure (up to 58 GPa) range hcp 4 He is stable with the exception of two narrow segments adjacent to the melting curve (25.9 -30.4 bar, bcc, and 0.1 -11.6 GPa, fcc). The highest volume compression reached in the equation of state (EOS) experiments is V 0 /V = 10.4 at 180 GPa for solid hydrogen 6 (V 0 /V = 7.6 for solid D 2 15 ), and V 0 /V = 8.4 for solid helium 13 . The phonon spectra of hcp hydrogen and helium exhibits a Raman-active optical mode of the E 2g symmetry. The frequency ν(P ) ...

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Sound velocities of hexagonal close-packed H2and He under pressure

et al. 2013

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“…H2 melting curve corresponds to Kechin equation [14]. Debye temperatures were calculated using the many-body potentials: for He and H2 [10,15], for Ne and Ar [16].…”

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“…The sound velocities for H 2 and He are given in Ref. [15]; the data for Ne by Gupta and Goyal were published in Ref. [19]; the data for Ar, Kr, and Xe will be published elsewhere.…”

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Poisson's ratio in cryocrystals under pressure

Freǐman

Grechnev

Tretyak

et al. 2015

Low Temperature Physics

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We present results of lattice dynamics calculations of Poisson's ratio (PR) for solid hydrogen and rare gas solids (He, Ne, Ar, Kr and Xe) under pressure. Using two complementary approaches -the semi-empirical many-body calculations and the first-principle density-functional theory calculations we found three different types of pressure dependencies of PR. While for solid helium PR monotonically decreases with rising pressure, for Ar, Kr, and Xe it monotonically increases with pressure. For solid hydrogen and Ne the pressure dependencies of PR are non-monotonic displaying rather deep minimums. The role of the intermolecular potentials in this diversity of patterns is discussed.

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“…Third, we used exactly the parametrization of pair and three-body forces as previously done in Refs. 31,[43][44][45][46] . Specifically, the pair potential (energy of a pair of H 2 molecules) is…”

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Elasticity and Poisson's ratio of hexagonal close-packed hydrogen at high pressures

et al. 2017

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International audienceThe elasticity at high pressure of solid hydrogen in hexagonal close-packed (hcp) phase I has been examined experimentally by laser acoustics technique in a diamond anvil cell, up to 55 GPa at 296 K, and theoretically using pair and three-body semiempirical potentials, up to 160 GPa. In the experiments on H2 and D2, the compressional sound velocity has been measured; the Poisson's ratio has been determined by combining these data with the previously reported equation of state. At room temperature, the difference between the adiabatic and isothermal processes vanishes above 25 GPa but cannot be neglected at lower pressure. Theoretically, all five elastic constants of hcp hydrogen have been calculated, and various derived elastic quantities are presented. The elastic anisotropy of hcp hydrogen was found to be significant, with ΔP ≈ 1.2, ΔS1 ≈ 1.7, and ΔS2 ≈ 1. Calculations suggest the Poisson's ratio to decrease with pressure reaching a minimum value of 0.28 at 145 GPa. In the experiment, the Poisson's ratio is also found to decrease with pressure. Theoretical calculations show that the inclusion of zero-point vibrations on the elastic properties of H2 does not result in any drastic changes of the behavior of the elastic quantities

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Sound velocities in solid hydrogen under pressure

Cited by 4 publications

References 46 publications

Sound velocities of hexagonal close-packed H2and He under pressure

Sound velocities of hexagonal close-packed H2and He under pressure

Poisson's ratio in cryocrystals under pressure

Elasticity and Poisson's ratio of hexagonal close-packed hydrogen at high pressures

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