Molecular rotation in <i>p</i>-H2 and <i>o</i>-D2 in phase I under pressure

Freǐman, Yu. A.; Tretyak, S. M.; Goncharov, Alexander F.; Mao, Ho‐kwang; Hemley, Russell J.

doi:10.1063/1.3674189

Cited by 10 publications

(7 citation statements)

References 18 publications

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“…At the same time, this distortion increases the contribution to the ground-state energy from the isotropic part of the intermolecular interaction. This contribution is quadratic in the lattice distortion parameter δ [52]. The loss in the isotropic part and the gain in the anisotropic part of the ground-state energy determines the lattice distortion parameter at the given molar volume.…”

Section: Hcp Lattice Distortion In Solid H 2 As a Function Of O-p Compositionmentioning

confidence: 99%

Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

Freiman

Crespo

2017

Low Temperature Physics

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The multiple isotopic family of hydrogens (H 2 , HD, D 2 , HT, DT, T 2 ) due to large differences in the de Boer quantum parameter and inertia moments displays a diversity of pronounced quantum isotopic solid-state effects. The homonuclear members of this family (H 2 , D 2 , T 2 ) due to the permutation symmetry are subjects of the constraints of quantum mechanics which link the possible rotational states of these molecules to their total nuclear spin giving rise to the existence of two spin-nuclear modifications, ortho-and parahydrogens, possessing substantially different properties. Consequently, hydrogen solids present an unique opportunity for studying both isotope and spin-nuclear effects. The rotational spectra of heteronuclear hydrogens (HD, HT, DT) are free from limitations imposed by the permutation symmetry. As a result, the ground state of these species in solid state is virtually degenerate. The most dramatic consequence of this fact is an effect similar to the Pomeranchuk effect in 3 He which in the case of the solid heteronuclear hydrogens manifests itself as the reentrant broken symmetry phase transitions. In this review article we discuss thermodynamic and kinetic effects pertaining to different isotopic and spin-nuclear species, as well as problems that still remain to be solved.

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Section: Hcp Lattice Distortion In Solid H 2 As a Function Of O-p Compositionmentioning

confidence: 99%

Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

Freiman

Crespo

2017

Low Temperature Physics

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“…The differences between the results obtained with the PBE and optB88-vdW functionals indicate some sensitivity to the functional used, which must temper our confidence in the accuracy of DFT results for this system. In addition, our simulations do not account for nuclear exchange effects such as those that occur in ortho and para molecules, which are known to be important in a quantitative description of phase I and its transition to phase II [44][45][46][47] . Notwithstanding these limitations, it is clear that quantum nuclear effects and molecular rotations play a very important role in the transition between phases I and II and the transition is strongly quantum in nature even when nuclear exchange is neglected.…”

Section: Discussionmentioning

confidence: 99%

Classical and quantum ordering of protons in cold solid hydrogen under megabar pressures

Walker

Probert

et al. 2013

J. Phys.: Condens. Matter

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A combination of state-of-the-art theoretical methods has been used to obtain an atomiclevel picture of classical and quantum ordering of protons in cold high-pressure solid hydrogen. We focus mostly on phases II and III of hydrogen, exploring the effects of quantum nuclear motion on certain features of these phases (through a number of ab initio path integral molecular dynamics (PIMD) simulations at particular points on the phase diagram).We also examine the importance of van der Waals forces in this system by performing calculations using the optB88-vdW density functional, which accounts for non-local correlations.Our calculations reveal that the transition between phases I and II is strongly quantum in nature, resulting from a competition between anisotropic inter-molecular interactions that restrict molecular rotation and thermal plus quantum fluctuations of the nuclear positions that facilitate it. The transition from phase II to III is more classical because quantum nuclear motion plays only a secondary role and the transition is determined primarily by the underlying potential energy surface. A structure of P 2 1 /c symmetry with 24 atoms in the primitive unit cell is found to be stable when anharmonic quantum nuclear vibrational motion is included at finite temperatures using the PIMD method. This structure gives a good account of the infra-red (IR) and Raman vibron frequencies of phase II. We find additional support for a C2/c structure as a strong candidate for phase III, since it remains transparent up to 300 GPa, even when quantum nuclear effects are included. Finally, we find that accounting for van der Waals forces improves the agreement between experiment and theory for the parts of the phase diagram considered, when compared to previous work which employed the widely-used Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional.arXiv:1302.0062v1 [cond-mat.mtrl-sci]

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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…”

Section: B Theorymentioning

confidence: 99%

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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Molecular rotation in p-H2 and o-D2 in phase I under pressure

Cited by 10 publications

References 18 publications

Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

Classical and quantum ordering of protons in cold solid hydrogen under megabar pressures

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

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