The anharmonicity of atomic motion limits the thermal conductivity in crystalline solids. However, a microscopic understanding of the mechanisms active in strong thermal insulators is lacking. In this letter, we classify 465 experimentally known materials with respect to their anharmonicity and perform fully anharmonic ab initio Green-Kubo calculations for 58 of them, finding 28 thermal insulators with $\kappa < 10$ W/mK including 6 with ultralow $\kappa \simeq 1$ W/mK. Our analysis reveals that the underlying strong anharmonic dynamics is driven by the exploration of meta-stable intrinsic defect geometries. This is at variance with the frequently applied perturbative approach, in which the dynamics is assumed to evolve around a single stable geometry.

中文翻译：

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热绝缘体的非谐性——从第一原理分析

原子运动的非谐性限制了结晶固体的热导率。然而，缺乏对强热绝缘体中活跃机制的微观理解。在这封信中，我们对 465 种实验已知材料的非谐性进行了分类，并对其中 58 种进行了完全非谐的从头算 Green-Kubo 计算，发现了 28 个 $\kappa < 10$ W/mK 的绝热体，其中 6 个具有超低 $\ kappa \simeq 1$ W/mK。我们的分析表明，潜在的强非谐动力学是由对亚稳态内在缺陷几何形状的探索所驱动的。这与经常应用的微扰方法不同，其中假设动力学围绕单个稳定的几何形状发展。