Dynamic Heterogeneity In The Monoclinic Phase Of CCl$_4$

TL;DR

This study uses molecular dynamics simulations to analyze the rotational heterogeneity in the monoclinic phase of CCl4, revealing jump-like rotations and fixed orientations linked to different rotational axes, akin to glassy relaxation features.

Contribution

It provides a detailed molecular-level understanding of rotational heterogeneity and dynamics in crystalline CCl4, connecting it to glass-like relaxation phenomena.

Findings

Rotational dynamics involve C3 jump-like rotations around C-Cl bonds.

Heterogeneous dynamics arise from different rotational axes with fixed orientations.

The master equation accurately describes the rotational behavior based on simulated rates.

Abstract

Carbon tetrachloride (CCl$_4$) is one of the simplest compounds having a translationally stable monoclinic phase while exhibiting a rich rotational dynamics below 226 K. Recent nuclear quadrupolar resonance (NQR) experiments revealed that the dynamics of CCl$_4$ is similar to that of the other members of the isostructural series CBr$_{n}$Cl$_{4-n}$, suggesting that the universal relaxation features of canonical glasses such as $\alpha$- and $\beta$-relaxation are also present in non-glass formers. Using molecular dynamics (MD) simulations we studied the rotational dynamics in the monoclinic phase of CCl$_4$. The molecules undergo $C3$ type jump-like rotations around each one of the four C-Cl bonds. The rotational dynamics is very well described with a master equation using as the only input the rotational rates measured from the simulated trajectories. It is found that the heterogeneous dynamics emerges from faster and slower modes associated with different rotational axes, which have fixed orientations relative to the crystal and are distributed among the four non-equivalent molecules of the unit cell.