The structure of binary Lennard-Jones clusters: The effects of atomic size ratio

TL;DR

This paper introduces a global optimization method to identify the most stable structures of binary Lennard-Jones clusters, revealing how atomic size ratio influences stability and structure, especially favoring polytetrahedral arrangements with core-shell geometries.

Contribution

It presents a new optimization approach for binary clusters and systematically maps stability and structure dependence on size ratio and cluster size.

Findings

Polytetrahedral structures are prevalent in stable binary clusters.

Size ratio influences the stabilization of core-shell geometries.

Structures with disclination lines are common in the parameter space.

Abstract

We introduce a global optimization approach for binary clusters that for a given cluster size is able to directly search for the structure and composition that has the greatest stability. We apply this approach to binary Lennard-Jones clusters, where the strength of the interactions between the two atom types is the same, but where the atoms have different sizes. We map out how the most stable structure depends on the cluster size and the atomic size ratio for clusters with up to 100 atoms and up to 30% difference in atom size. A substantial portion of this parameter space is occupied by structures that are polytetrahedral, both those that are polyicosahedral and those that involve disclination lines. Such structures involve substantial strains for one-component Lennard-Jones clusters, but can be stabilized by the different-sized atoms in the binary clusters. These structures often have a `core-shell' geometry, where the larger atoms are on the surface, and the smaller atoms are in the core.