# Berlin 2018 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 56: New materials and concepts

### HL 56.4: Vortrag

### Freitag, 16. März 2018, 12:00–12:15, EW 202

**Strong Anharmonic and Quantum-Nuclear Effects in the Low Temperature Dyamics of CsCl** — •Hagen-Henrik Kowalski, Matthias Scheffler, and Christian Carbogno — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin

In solid-state theory, the *quasi-harmonic* approximation is generally expected to hold for the description of the nuclear dynamics in crystals at temperatures ≪ 300 K. However, a recent experimental study [1] of single crystalline CsCl reveals that its thermal conductivity is comparable to those of amorphous materials (∼1 W/mK). Strong anharmonic effects hence appear to be active even at 50 K, a temperature at which the quantum-statistics for the nuclei is not negligible (*C*_{V} < 65% of the Dulong-Petit value). Using first-principles calculations, we investigate the nature of these effects by performing fully anharmonic molecular dynamics with *classical* nuclei (MD) and path-integral MD simulations with *quantum* nuclei. The comparison with respective *quasi-harmonic* calculations confirms that pronounced quantum-nuclear and anharmonic effects are active in this material and reveals how the respective mechanisms couple. Eventually, we discuss how these effects can affect simulations of the thermal conductivity [2] and the resulting implications for simulations across material space.

[1] M. Sist, *et al.*, *Ang. Chemie* **56**, 3625 (2017).

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