2015/02/10 by Ion Errea, Matteo Calandra, Chris J . Pickard +7 · 1 citation
Physics and Astronomy · #cond-mat.supr-con #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevlett.114.157004
published as Phys. Rev. Lett. 114, 157004 (2015) · 5 pages + supplemental material
arxiv created 2015/02/10 · arxiv updated 2015/04/22
We use first principles calculations to study structural, vibrational and superconducting properties of H2S at pressures P≥ 200 GPa. The inclusion of zero point energy leads to two different possible dissociations of H2S, namely 3H2S → 2H3S + S and 5H2S → 3H3S + HS2, where both H3S and HS2 are metallic. For H3S, we perform non-perturbative calculations of anharmonic effects within the self-consistent harmonic approximation and show that the harmonic approximation strongly overestimates the electron-phonon interaction (λ≈ 2.64 at 200 GPa) and Tc. Anharmonicity hardens HS bond-stretching modes and softens H--S bond-bending modes. As a result, the electron-phonon coupling is suppressed by 30% (λ≈ 1.84 at 200 GPa). Moreover, while at the harmonic level Tc decreases with increasing pressure, the inclusion of anharmonicity leads to a Tc that is almost independent of pressure. High pressure hydrogen sulfide is a strongly anharmonic superconductor.