Computational Study on Homogeneous Melting of Benzene Phase I

Abstract

Molecular-dynamics simulations are used for examining the microscopic details of the homogeneous melting of benzene phase I. The equilibrium melting temperatures of our model were initially determined using the direct-coexistence method. Homogeneous melting at a higher temperature is achieved by heating a defect-and surfacefree crystal. The temperature-dependent potential energy and lattice parameters do not indicate a premelting phase even under superheated conditions. Further, statistical analyses using induction times computed from 200 melting trajectories were conducted, denoting that the homogeneous melting of benzene occurs stochastically, and that there is no intermediate transient state between the crystal and liquid phases. Additionally, the critical nucleus size is estimated using the seeding approach, along with the local bond order parameter. We found that the large diffusive motion arising from defect migration or neighbor-molecule swapping is of little importance during nucleation. Instead, the orientational disorder activated using the flipping motion of the benzene plane results in the melting nucleus.

Stepwise Homogeneous Melting of Benzene Phase I at High Pressure

“…These results indicate that all molecules change the orientations in the transition from phase I to the metastable phase. In the previous study, we have shown that at ambient pressure the flipping motion played an important role in the formation of the critical nucleus [32]. Hence, the rotational motion triggers the melting transition of phase I at both the pressures.…”

“…This premelting stage was later disproven by the investigation over the complete temperature range of 4 to 280 K [31]. Very recently, 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.…”