Black metal hydrogen above 360 GPa driven by proton quantum fluctuations

Monacelli, Lorenzo; Errea, Ion; Calandra, Matteo; Mauri, Francesco

doi:10.1038/s41567-020-1009-3

Cited by 56 publications

(52 citation statements)

References 43 publications

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“…Let a and b be indexes that label both an atom in the crystal and a Cartesian direction. However, it has been shown recently that quantum ionic fluctuations and the consequent anharmonicity can have a huge impact both on the crystal structure and the phonon [25,[28][29][30][31][32][33][34][35], due to the lightness of hydrogen. Interestingly, these effects can both strongly enhance or suppress the predicted critical temperature.…”

Section: Introductionmentioning

confidence: 99%

Quantum anharmonic enhancement of superconductivity in P63/mmc ScH6 at high pressures: A first-principles study

Hou

Belli

Bianco

et al. 2021

Journal of Applied Physics

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Making use of first-principles calculations, we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of P 63/mmc ScH6 in the 100-160 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a strong correction to the crystal structure, the phonon spectra, and the superconducting critical temperatures, which have been estimated in previous calculations without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for the lattice dynamics. Quantum ionic fluctuations have a large impact on the H2 molecular-like units present in the crystal by increasing the hydrogen-hydrogen distance about a 5%. According to our anharmonic phonon spectra, this structure will be dynamically stable at least above 85 GPa, which is 45 GPa lower than the pressure given by the harmonic approximation. Contrary to many superconducting hydrogen-rich compounds, where quantum ionic effects and the consequent anharmonicity tend to lower the superconducting critical temperature, our results show that it can be enhanced in P 63/mmc ScH6 by approximately 15%. We attribute the enhancement of the critical temperature to the stretching of the H2 molecular-like units and the associated increase of the electron-phonon interaction. Our results suggest that quantum ionic effects increase the superconducting critical temperature in hydrogen-rich materials with H2 units by increasing the hydrogen-hydrogen distance and, consequently, the electron-phonon interaction.

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Section: Introductionmentioning

confidence: 99%

Quantum anharmonic enhancement of superconductivity in P63/mmc ScH6 at high pressures: A first-principles study

Hou

Belli

Bianco

et al. 2021

Journal of Applied Physics

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“…For instance, many of them simply correct the free energy and/or the phonon frequencies assuming that the ions remain fixed at the R 0 classical positions. However, as it has been shown recently in several compounds [34][35][36][37], the ionic positions can be strongly altered by quantum effects and anharmonicity even at zero Kelvin. The structural changes are important for both internal degrees of freedom (the Wyckoff positions), and the lattice parameters themselves.…”

Section: Introductionmentioning

confidence: 91%

“…For instance, the experimental crystal structure of both H 3 S and LaH 10 compounds is stable thanks to quantum effects in the pressure range where they highest superconducting critical temperatures have been experimentally observed [34,36]. A large modification of the structure of molecular phases of hydrogen has also been predicted within the SSCHA, which is crucial to understand the experimental Raman and infrared spectra [35,37]. The change in the crystal structure that the SSCHA captures goes beyond The SSCHA auxiliary phonon frequencies are given, those obtained diagonalizing Φ eq , together with the phonon frequencies obtained from the spectal function in the Lorentzian approximation.…”

Section: Hydrogen-based Compoundsmentioning

confidence: 97%

The stochastic self-consistent harmonic approximation: calculating vibrational properties of materials with full quantum and anharmonic effects

Monacelli

Bianco

Cherubini

et al. 2021

J. Phys.: Condens. Matter

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137

114

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The efficient and accurate calculation of how ionic quantum and thermal fluctuations impact the free energy of a crystal, its atomic structure, and phonon spectrum is one of the main challenges of solid state physics, especially when strong anharmonicy invalidates any perturbative approach. To tackle this problem, we present the implementation on a modular Python code of the stochastic self-consistent harmonic approximation (SSCHA) method. This technique rigorously describes the full thermodynamics of crystals accounting for nuclear quantum and thermal anharmonic fluctuations. The approach requires the evaluation of the Born-Oppenheimer energy, as well as its derivatives with respect to ionic positions (forces) and cell parameters (stress tensor) in supercells, which can be provided, for instance, by first principles density-functional-theory codes. The method performs crystal geometry relaxation on the quantum free energy landscape, optimizing the free energy with respect to all degrees of freedom of the crystal structure. It can be used to determine the phase diagram of any crystal at finite temperature. It enables the calculation of phase boundaries for both first-order and * Authors to whom any correspondence should be addressed.Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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“…The importance of ionic quantum fluctuations can be ascribed trivially to the presence of hydrogen in the system, the lightest atom in the periodic table and, consequently, the one which is more prone to quantum fluctuations. Several other hydrogen-rich compounds [5,[38][39][40][41] and solid hydrogen itself [42,43] are also largely affected by such effects. There is, however, another less apparent but very important point that makes ionic quantum effects crucial in high-T c superconducting hydrides: their huge electron-phonon coupling induces large phonon instabilities in the harmonic approximation.…”

Section: The Ultimate Goalmentioning

confidence: 99%

Superconducting hydrides on a quantum landscape

Errea

2022

Preprint

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Reaching superconductivity at ambient conditions is one of the biggest scientific dreams. The discoveries in the last few years at high pressures place hydrogen-based compounds as the best candidates for making it true. As the recent history shows, first-principles calculations are expected to continue guiding the experimental quest in the right track in the coming years. Considering that ionic quantum fluctuations largely affect the structural and vibrational properties of superconducting hydrides, in many cases making them stable at much lower pressures than expected, it will be crucial to include such effects on the future ab initio predictions. The prospects for low-pressure high critical-temperature compounds are wide open, even at ambient pressure.

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Black metal hydrogen above 360 GPa driven by proton quantum fluctuations

Cited by 56 publications

References 43 publications

Quantum anharmonic enhancement of superconductivity in P63/mmc ScH6 at high pressures: A first-principles study

Quantum anharmonic enhancement of superconductivity in P63/mmc ScH6 at high pressures: A first-principles study

The stochastic self-consistent harmonic approximation: calculating vibrational properties of materials with full quantum and anharmonic effects

Superconducting hydrides on a quantum landscape

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