Strongly first order melting of a two dimensional molecular solid

TL;DR

This study uses computer simulations to explore the melting behavior of a two-dimensional molecular solid, revealing a strongly first-order transition and complex defect structures, contrasting with traditional theories.

Contribution

It provides new insights into the melting of 2D molecular solids, showing a one-step first-order transition and complex defect behavior, which differ from atomic system studies.

Findings

First-order melting transition observed for both crystalline phases.

Rich phase diagram including honeycomb and oblique solids.

Complex defect structures near melting transition.

Abstract

Melting and freezing transitions in two dimensional systems are known to show highly unusual characteristics. Most of the earlier studies considered atomic systems; the melting behavior in two dimensional molecular solids is still largely unexplored. In order to understand the role of multiple energy and length scales present in molecular systems on nature of melting transition, here we report computer simulation studies of melting of a two dimensional Mercedes-Benz (MB) system. We find that the interplay between the strength of isotropic and anisotropic interactions can give rise to rich phase diagram. The computed solid-liquid phase diagram consists of isotropic liquid and two crystalline phases - honeycomb and oblique. In contradiction to the celebrated KTHNY theory, we observe strongly one step first order melting transitions for both the honeycomb and oblique solids. The defects in both solids and liquids near the transition are more complex compared to the atomic systems.