Anisotropic Displacement Parameters of Ba2 in Clathrate Structure Ba₈Ga₁₆Ge₃₀ from Molecular Dynamics Simulations

Atomic displacement parameters (ADPs) are crystallographic structural data that may represent atomic motion, possible static displacive disorder, and thermal vibration. Thermoelectric materials often contain rattling atoms to improve performance, and ADPs describe how atoms rattle. This paper discusses the ADPs of the Ba2 site of Ba8Ga16Ge30, a clathrate structure thermoelectric material. A molecular dynamics simulation approach using a neural network potential was applied to Ba8Ga16Ge30 models considering the disorder of Ga and Ge on the Ga/Ge cage sites. The calculated U is non-zero when extrapolated to 0 K, overestimates experimental U11 by 0.005-0.009 Å2 at temperatures between 200 and 300 K, and overestimates experimental U22 by 0.010-0.014 Å2 between 15 and 300 K.