高压下 I-43m CH4-H3S 超导性的量子非谐效应：第一性原理研究
Quantum Anharmonic Effects on the Superconductivity of I-43m CH4-H3S at High Pressures: a First-Principles Study
AI总结：
本文利用第一性原理计算，研究了 150-300 GPa 下量子离子涨落和晶格非谐性对 I-43m CH4-H3S 结构与超导性的影响，发现非谐效应使电子-声子耦合常数在 200 GPa 时被抑制 46%，超导临界温度被高估约 50 K。
AI中文摘要：
利用第一性原理计算，我们在随机自洽谐和近似（stochastic self-consistent harmonic approximation）框架内，分析了 150-300 GPa 压力范围内量子离子涨落和晶格非谐性对 I-43m CH4-H3S（C-S-H 体系中焓值最低的结构之一）晶体结构和超导性的影响。我们预测了对晶体结构（由 H3S 晶格和 CH4 分子组成）、声子谱以及压力依赖的超导临界温度的修正，这些量在先前的计算中已被估算，但未考虑晶体结构上的离子涨落，并假设晶格动力学服从谐和近似。我们的结果表明，量子离子涨落影响 H3S 主晶格中 H 原子与 S 原子间的距离，促使其形成更对称的键，而甲烷分子几乎不受影响。根据我们的非谐声子谱，该结构在 150 GPa 以上动力学稳定，这比谐和近似预测出现不稳定性的压力低 30 GPa。由于声子频率的强烈非谐增强，电子-声子耦合常数在 200 GPa 时被抑制了 46%，在更低压力下抑制更强。结果，200 GPa 时的超导临界温度被高估了约 50 K，导致其在所研究的整个压力范围内降至 150 K 以下。我们的结果强调，三元氢化物在结构、振动和超导性质上受到强烈的非谐效应影响。
英文摘要：
Making use of first-principles calculations we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of I-43m CH4-H3S, one of the lowest enthalpy structures in the C-S-H system, in the 150-300 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a correction to the crystal structure, which is formed by an H3S lattice and CH4 molecules, the phonon spectra, and the pressure-dependent 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. Our results show that quantum ionic fluctuations have an impact on the distance between H atoms and S atoms in the H3S host lattice, pushing it towards more symmetric bonds, while the methane molecules are barely affected. According to our anharmonic phonon spectra, this structure is dynamically stable above 150 GPa, which is 30 GPa lower than the pressure at which the harmonic approximation predicts the emergence of an instability. As a consequence of the strong anharmonic enhancement of the phonon frequencies, the electron-phonon coupling constant is suppressed by 46% at 200 GPa, and even more at lower pressures. As a result, the superconducting critical temperature is overestimated by around 50 K at 200 GPa, such that it falls below 150 K in the whole pressure range studied. Our results underline that ternary hydrides are subject to strong anharmonic effects on their structural, vibrational, and superconducting properties.
