Structural Diagram of AuxCu1−x Nanoparticles: Dependency of Geometry on Composition and Size

Abstract

In this article, we describe a systematic molecular dynamics study of Au–Cu nanoparticles covering an ample range of sizes, elemental distributions, and relative concentrations. The interatomic interactions were described through the quantum version of the Sutton and Chen potential. Cuboctahedral particles were subjected to a heating process until reaching 2000 K, to be cooled down afterwards well below the liquid-to-solid transition. We found the dependence of the melting point with respect to the relative concentration of Au and Cu on the nanoparticles as well as its dependence with the size of the particles. We performed a structural analysis of the final configurations based on the bond order parameter, which takes a specific value depending on the geometry and crystalline structure of the particle. We found that after the heating and cooling cycle, icosahedral structures were more preponderant for particles below 5 nm in size, while truncated octahedra prevailed for larger sizes. The results were used to build a structural diagram for the particles, where we locate the most favorable geometries in function of the relative concentrations of the two metals and the size of the particles.