We present first-principles calculations of metallic atomic hydrogen in the 400-600 GPa pressure range in a tetragonal structure with space group I4(1)/amd, which is predicted to be its first atomic phase. Our calculations show a band structure close to the free-electron-like limit due to the high electronic kinetic energy induced by pressure. Bands are properly described even in the independent electron approximation fully neglecting the electron-electron interaction. Linear-response harmonic calculations show a dynamically stable phonon spectrum with marked Kohn anomalies. Even if the electron-electron interaction has a minor role in the electronic bands, the inclusion of electronic exchange and correlation in the density response is essential to obtain a dynamically stable structure. Anharmonic effects, which are calculated within the stochastic self-consistent harmonic approximation, harden high-energy optical modes and soften transverse acoustic modes up to a 20% in energy. Despite a large impact of anharmonicity has been predicted in several high-pressure hydrides, here the superconducting critical temperature is barely affected by anharmonicity, as it is lowered from its harmonic 318 K value only to 300 K at 500 GPa. We attribute the small impact of anharmonicity on superconductivity to the absence of softened optical modes and the fairly uniform distribution of the electron-phonon coupling among the vibrational modes.

Anharmonic effects in atomic hydrogen: Superconductivity and lattice dynamical stability / Borinaga, Miguel; Errea, Ion; Calandra, Matteo; Mauri, Francesco; Bergara, Aitor. - In: PHYSICAL REVIEW. B. - ISSN 2469-9950. - 93:17(2016). [10.1103/PhysRevB.93.174308]

Anharmonic effects in atomic hydrogen: Superconductivity and lattice dynamical stability

MAURI, FRANCESCO;
2016

Abstract

We present first-principles calculations of metallic atomic hydrogen in the 400-600 GPa pressure range in a tetragonal structure with space group I4(1)/amd, which is predicted to be its first atomic phase. Our calculations show a band structure close to the free-electron-like limit due to the high electronic kinetic energy induced by pressure. Bands are properly described even in the independent electron approximation fully neglecting the electron-electron interaction. Linear-response harmonic calculations show a dynamically stable phonon spectrum with marked Kohn anomalies. Even if the electron-electron interaction has a minor role in the electronic bands, the inclusion of electronic exchange and correlation in the density response is essential to obtain a dynamically stable structure. Anharmonic effects, which are calculated within the stochastic self-consistent harmonic approximation, harden high-energy optical modes and soften transverse acoustic modes up to a 20% in energy. Despite a large impact of anharmonicity has been predicted in several high-pressure hydrides, here the superconducting critical temperature is barely affected by anharmonicity, as it is lowered from its harmonic 318 K value only to 300 K at 500 GPa. We attribute the small impact of anharmonicity on superconductivity to the absence of softened optical modes and the fairly uniform distribution of the electron-phonon coupling among the vibrational modes.
2016
SOLID HYDROGEN; METALLIC HYDROGEN; DENSE HYDROGEN; HIGH-PRESSURES; PHASE; GPA; TEMPERATURE; GIGAPASCALS; VIBRATIONS; ELECTRONS
01 Pubblicazione su rivista::01a Articolo in rivista
Anharmonic effects in atomic hydrogen: Superconductivity and lattice dynamical stability / Borinaga, Miguel; Errea, Ion; Calandra, Matteo; Mauri, Francesco; Bergara, Aitor. - In: PHYSICAL REVIEW. B. - ISSN 2469-9950. - 93:17(2016). [10.1103/PhysRevB.93.174308]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/953423
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