The role of FCC tetrahedral subunits in the phase behavior of medium sized Lennard-Jones clusters

TL;DR

This study investigates the free energy landscape and structural transformations of 600-atom Lennard-Jones clusters, revealing the role of FCC tetrahedral subunits in phase behavior and nucleation processes.

Contribution

It introduces a detailed analysis of FCC tetrahedral subunits' influence on phase transitions in medium-sized Lennard-Jones clusters, combining free energy calculations and molecular dynamics simulations.

Findings

Identification of multiple free energy minima corresponding to different structural phases.

Observation of nucleation events leading to various tetrahedral structures in the cluster core.

Correlation between tetrahedral subunit formation and phase behavior in clusters.

Abstract

The free energy of a 600-atom Lennard-Jones cluster is calculated as a function of surface and bulk crystallinity in order to study the structural transformations that occur in the core of medium sized clusters. Within the order parameter range studied, we find the existence of two free energy minima at temperatures near freezing. One minimum, at low values of both bulk and surface order, belongs to the liquid phase. The second minimum exhibits a highly ordered core with a disordered surface and is related to structures containing a single FCC-tetrahedral subunit, with an edge length of seven atoms (l=7), located in the particle core. At lower temperatures, a third minimum appears at intermediate values of the bulk order parameter which is shown to be related to the formation of multiple l=6 tetrahedra in the core of the cluster. We also use molecular dynamics simulations to follow a series of nucleation events and find that the clusters freeze to structures containing l=5,6,7 and 8 sized tetrahedra as well as those containing no tetrahedral units. The structural correlations between bulk and surface order with the size of the tetrahedral units in the cluster core are examined. Finally, the relationships between the formation of FCC tetrahedral subunits in the core, the phase behavior of medium sized clusters and the nucleation of noncrystalline global structures such as icosahedra and decahedra are discussed.