High-Pressure Behavior of Hydrogen and Deuterium at Low Temperatures

Liu, Xiao-Di; Howie, Ross T.; Zhang, Huichao; Chen, Xiao‐Jia; Gregoryanz, Eugene

doi:10.1103/physrevlett.119.065301

Cited by 24 publications

(32 citation statements)

References 33 publications

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“…5). The phase boundary agrees well with the experiment 32 , particularly for the more classically behaved deuterium. Similarity to experiments on deuterium rather than hydrogen is perhaps unsurprising, since nuclear quantum effects such as zero-point motion are significant at the low temperatures investigated here.…”

Section: à ásupporting

confidence: 85%

“…This methodology, whether based on DFT or QMC, predicts hcp-like ground states for Phases I-III in agreement with X-ray data. However the spectroscopic signature of the Phase II-the appearance of many sharp, low-frequency, and peaks 11,32 -is not well reproduced by the quasiharmonic calculations. As explained in the previous paragraph, the likely cause is a failure of the harmonic mode assumption for excited states, rather than the DFT itself.…”

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confidence: 86%

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Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

2020

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The hydrogen phase diagram has several unusual features which are well reproduced by density functional calculations. Unfortunately, these calculations do not provide good physical insights into why those features occur. Here, we present a fast interatomic potential, which reproduces the molecular hydrogen phases: orientationally disordered Phase I; broken-symmetry Phase II and reentrant melt curve. The H2 vibrational frequency drops at high pressure because of increased coupling between neighbouring molecules, not bond weakening. Liquid H2 is denser than coexisting close-packed solid at high pressure because the favored molecular orientation switches from quadrupole-energy-minimizing to steric-repulsion-minimizing. The latter allows molecules to get closer together, without the atoms getting closer, but cannot be achieved within in a close-packed layer due to frustration. A similar effect causes negative thermal expansion. At high pressure, rotation is hindered in Phase I, such that it cannot be regarded as a molecular rotor phase.

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confidence: 85%

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confidence: 86%

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

2020

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“…These recent developments pave the path towards NMR spectroscopy experiments in the pressure range relevant for high pressure hydrogen phases II-VI. Phase II of hydrogen first appears at pressures in the range 73-110 GPa [20][21][22], and that of deuterium at even lower pressures of about 25 GPa [23]. Phase III appears in the pressure range 150-170 GPa [24], and phase IV in the pressure range 200-220 GPa [25].…”

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confidence: 99%

Nuclear Magnetic Resonance Spectroscopy as a Dynamical Structural Probe of Hydrogen under High Pressure

2019

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An unambiguous crystallographic structure solution for the observed phases II-VI of high pressure hydrogen does not exist due to the failure of standard structural probes at extreme pressure. In this work we propose that nuclear magnetic resonance spectroscopy provides a complementary structural probe for high pressure hydrogen. We show that the best structural models available for phases II, III, and IV of high pressure hydrogen exhibit markedly distinct nuclear magnetic resonance spectra which could therefore be used to discriminate amongst them. As an example, we demonstrate how nuclear magnetic resonance spectroscopy could be used to establish whether phase III exhibits polymorphism. Our calculations also reveal a strong renormalisation of the nuclear magnetic resonance response in hydrogen arising from quantum fluctuations, as well as a strong isotope effect. As the experimental techniques develop, nuclear magnetic resonance spectroscopy can be expected to become a useful complementary structural probe in high pressure experiments.

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“…H/D isotopic effects have been discussed in the four crystal structures of the molecular solid observed so far, namely phases I, II, III and IV. These studies have shown that the phase I/II boundary has a strong isotope dependence, whereas the phase II/III boundary is almost identical for H and D [76][77][78][79][80][81][82][83]. In phase I, the H 2 molecules rotate freely, following the quantum rotational partition 6 function [84], whereas in phase II the hydrogen molecules are preferentially aligned on their crystalline lattice sites [85].…”

Section: Quantum Nature Of Condensed Phase Hydrogenmentioning

confidence: 99%

The quantum nature of hydrogen

Fang

Chen

Feng

et al. 2019

International Reviews in Physical Chemistry

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Hydrogen is the most abundant element. It is also the most quantum, in the sense that quantum tunnelling, quantum delocalisation, and zero-point motion can be important. For practical reasons most computer simulations of materials have not taken such effects into account, rather they have treated nuclei as classical particles. However, thanks to methodological developments over the last few decades, nuclear quantum effects can now be treated in complex materials. Here we discuss our studies on the role nuclear quantum effects play in hydrogen containing systems. We give examples of how the quantum nature of the nuclei has a significant impact on the location of the boundaries between phases in high pressure condensed hydrogen. We show how nuclear quantum effects facilitate the dissociative adsorption of molecular hydrogen on solid surfaces and the diffusion of atomic hydrogen across surfaces. Finally, we discuss how nuclear quantum effects alter the strength and structure of hydrogen bonds, including those in DNA. Overall these studies demonstrate that nuclear quantum effects can manifest in different, interesting, and non-intuitive ways. Whilst historically it has been difficult to know in advance what influence nuclear quantum effects will have, some of the important conceptual foundations have now started to emerge.

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High-Pressure Behavior of Hydrogen and Deuterium at Low Temperatures

Cited by 24 publications

References 33 publications

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

Nuclear Magnetic Resonance Spectroscopy as a Dynamical Structural Probe of Hydrogen under High Pressure

The quantum nature of hydrogen

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