Identifying thermal insulators via ab initio Green Kubo simulations guided by anharmonicity*

We present a systematic first-principles search for thermal insulators in material space, covering hundreds of compounds, five lattice types and seven space groups, including simple rocksalt and zinc blende structures up to complex perovskites with 20 atoms per unit cell. Using the high-throughput framework FHI-vibes [1,2] and a recently developed measure for the strength of anharmonicity [3], we identify 120 candidate materials with potential for ultra-low thermal conductivity <2 W/mK at room temperature, i.e., comparable to those of thermoelectrics such as SnSe or MgSb. We perform non-perturbative ab initio Green-Kubo simulations [4] for the 60 most promising candidates, thereby including all anharmonic effects responsible for low thermal conductivity.

With this approach, we identify seven new compounds with calculated ultra-low thermal conductivity. We analyze the underlying dynamical mechanisms, in particular the importance of strong anharmonic effects not accessible in perturbative phonon formalisms, e.g., short-lived metastable configurations and precursors of structural phase transitions. Eventually, we discuss the relevance of ab initio Green-Kubo methods for the discovery of novel, anharmonic, and increasingly complex materials.

[1] F. Knoop et al., J. Open Source Softw. 5, 2671 (2020)

[2] V. Blum et al., Comput. Phys. Commun. 180, 2175 (2009)

[3] F. Knoop, et al., Phys. Rev. Mater. 4, 083809 (2020)

[4] C. Carbogno, R. Ramprasad, and M. Scheffler, Phys. Rev. Lett. 118, 175901 (2017)