Dynamic heterogeneity in an orientational glass

TL;DR

This study uses molecular dynamics simulations to investigate the microscopic reorientational jump motions in CBrCl3, revealing cage-orientational jumps similar to supercooled liquids and explaining relaxation times through microscopic mechanisms.

Contribution

It provides detailed insights into the microscopic reorientational dynamics and relaxation mechanisms in CBrCl3, linking molecular jumps to experimental relaxation times.

Findings

Molecules perform reorientational discrete jumps exchanging equivalent positions.

Correlation times match previous dielectric measurements.

Two groups of molecules exhibit longer characteristic times.

Abstract

Family of compounds CBr$_n$Cl$_{4-n}$ has been proven helpful in unraveling microscopic mechanisms responsible of glassy behavior. Some of the family members show translational ordered phases with minimal disorder which appears to reveal glassy features, thus deserving special attention in the search for universal glass anomalies. In this work, we studied CBrCl$_3$ dynamics by performing extensive molecular dynamics simulations. Molecules of this compound perform reorientational discrete jumps, where the atoms exchange equivalent positions among each other revealing a cage-orientational jump motion fully comparable to the cage-rototranslational jump motion in supercooled liquids. Correlation times were calculated from rotational autocorrelation functions showing good agreement with previous reported dielectric results. From mean waiting and persistence times calculated directly from trajectory results, we are able to explain which microscopic mechanisms lead to characteristic times associated with $\alpha$ and $\beta$-relaxation times measured experimentally. We found that two nonequivalent groups of molecules have a longer characteristic time than the other two nonequivalent groups, both of them belonging to the asymmetric unit of the monoclinic (C2/c) lattice.