Stepwise Homogeneous Melting of Benzene Phase I at High Pressure

Ravi Mahesta,Kenji Mochizuki

doi:10.3390/cryst9060279

Abstract

We investigate, using molecular dynamics simulations, the spontaneous homogeneous melting of benzene phase I under a high pressure of 1.0 GPa. We find an apparent stepwise transition via a metastable crystal phase, unlike the direct melting observed at ambient pressure. The transition to the metastable phase is achieved by rotational motions, without the diffusion of the center of mass of benzene. The metastable crystal completely occupies the whole space and maintains its structure for at least several picoseconds, so that the phase seems to have a local free energy minimum. The unit cell is found to be unique—no such crystalline structure has been reported so far. Furthermore, we discuss the influence of pressure control on the melting behavior.

Highlights

Benzene is a renowned small and simple molecule
We performed the molecular dynamics (MD) simulations for the homogeneous melting of benzene phase I crystal near the limit of superheating and statistically demonstrated that there is no intermediate transient state between the crystal and liquid phases [32]
We initially evaluated the equilibrium melting temperature Tm of benzene phase I at 1.0 GPa in

Summary

Introduction

Benzene is a renowned small and simple molecule. Regardless, its polymorphism [1,2,3] and local liquid structure [4,5,6] have been extensively explored until now. We performed the molecular dynamics (MD) simulations for the homogeneous melting of benzene phase I crystal near the limit of superheating and statistically demonstrated that there is no intermediate transient state between the crystal and liquid phases [32]. While these studies have been conducted under ambient pressure, the melting dynamics under high pressure have not been explored. We perform MD simulations of the homogeneous melting of benzene phase I at a high pressure of 1.0 GPa and observe the stepwise transition via a metastable crystal phase. We show that the formation of the metastable phase is achieved by rotational motions, and the unit cell structure differs from any other crystalline phases reported so far

Force Field

MD Simulations

Crystals

Results and Discussion