Structural transitions in the 309-atom magic number Lennard-Jones cluster

TL;DR

This study investigates the thermal behavior and structural transitions of a 309-atom Lennard-Jones cluster, revealing pronounced peaks in heat capacity linked to surface roughening and large-scale structural transformations.

Contribution

It provides new insights into the structural transitions and surface reconstructions in magic number Lennard-Jones clusters using parallel tempering Monte Carlo simulations.

Findings

Pronounced heat capacity peak before melting.

Surface roughening involves vacancy and adatom condensation.

Formation of twinned structures with face-centered cubic tetrahedra.

Abstract

The thermal behaviour of the 309-atom Lennard-Jones cluster, whose structure is a complete Mackay icosahedron, has been studied by parallel tempering Monte Carlo simulations. Surprisingly for a magic number cluster, the heat capacity shows a very pronounced peak before melting, which is attributed to several coincident structural transformation processes. The main transformation is somewhat akin to surface roughening, and involves a cooperative condensation of vacancies and adatoms that leads to the formation of pits and islands one or two layers thick on the Mackay icosahedron. The second transition in order of importance involves a whole scale transformation of the cluster structure, and leads to a diverse set of twinned structures that are assemblies of face-centred-cubic tetrahedra with 6 atoms along their edges, i.e., one atom more than the edges of the 20 tetrahedra that make up the 309-atom Mackay icosahedron. A surface reconstruction of the icosahedron from a Mackay to an anti-Mackay overlayer is also observed, but with a lower probability.