Two-dimensional melting in simple atomic systems: continuous vs. discontinous melting

TL;DR

This study uses molecular dynamics simulations to explore how the range of interatomic potentials influences the nature of two-dimensional melting, revealing a crossover from continuous to discontinuous transitions.

Contribution

It demonstrates how potential range affects melting behavior, showing stable hexatic phases with longer-range potentials and first-order transitions with shorter-range potentials.

Findings

Longer-range potentials exhibit stable hexatic phases.

Shorter-range potentials show first-order melting transitions.

Intermediate-range potentials display mixed features with weakly first-order behavior.

Abstract

We investigate the characteristics of two dimensional melting in simple atomic systems via isobaric-isothermal ($NPT$) and isochoric-isothermal ($NVT$) molecular dynamics simulations with special focus on the effect of the range of the potential on the melting. We find that the system with interatomic potential of longer range clearly exhibits a region (in the $PT$ plane) of (thermodynamically) stable hexatic phase. On the other hand, the one with shorter range potential exhibits a first-order melting transition both in $NPT$ and $NVT$ ensembles. Melting of the system with intermediate range potential shows a hexatic-like feature near the melting transition in $NVT$ ensemble, but it undergoes an unstable hexatic-like phase during melting process in $NPT$ ensemble, which implies existence of a weakly first order transition. The overall features represent a crossover from a continuous melting transition in the cases of longer-ranged potential to a discontinuous (first order) one in the systems with shorter and intermediate ranged potential. We also calculate the Binder cumulants as well as the susceptibility of the bond-orientational order parameter.