Crystallization of the Lewis-Wahnstr\"{o}m ortho-terphenyl model

TL;DR

This study observes crystallization in molecular dynamics simulations of a bent trimer model for ortho-terphenyl, revealing structural and dynamic properties of the resulting crystal and insights into its glass-forming ability.

Contribution

It provides the first detailed simulation-based analysis of crystallization and crystal structure in the Lewis-Wahnström ortho-terphenyl model.

Findings

Crystals form with molecules near BCC lattice sites.

Orientational disorder with cubatic order observed.

Modest decreases in mobility upon crystallization.

Abstract

Crystallization is observed during long molecular dynamics simulations of bent trimers, a molecular model proposed by Lewis and Wahnstr\"{o}m for ortho-terphenyl. In the crystal, the three spheres that make up the rigid molecule sit near sites of a body centered cubic lattice, the trimer bond angle being almost optimal for this structure. The crystal exhibits orientational disorder with the molecules aligned randomly along the three Cartesian axis (an example of cubatic orientational order). The rotational and translational mobilities exhibit only modest decreases on crystallization, by factors of 10 and 3 respectively. The rotational relaxation does change from Debye-like in the liquid to large angle jumps in the crystal. We consider the origin of the superior glass forming ability of the the trimer over the monatomic liquid.