Molecular Simulation Of Au-Pd And Au-Pd-Pt Metallic Clusters

Bimetallic nanoparticles and trimetallic nanoparticles have received considerable attention from the scientific community because of their unique physical and chemical properties. Nanoparticles generally posses different properties from bulk materials as a result of their large surface to volume ratio. Surface segregation phenomena and meting temperature depression are two of their well-known properties.Atomic ordering (segregation or mixing) is essential for both bimetallic clusters and and trimetallic nanoparticles, because the chemical and physical properties of these clusters can be tuned. Also, the thermal properties of these clusters are even more complex than that of the elemental ones. First, compared with the elemental metal clusters, bimetallic clusters and trimetallic nanoparticles may display some specific properties. Second, their properties depend not only on size but also on composition and atomic ordering. In the past few decades, many experiments have provided theoretical evidence of melting temperature depression and surface segregation, but the experiments consumed an immense amount of time and effort.Understanding the structural properties and thermodynamics of bimetallic clusters and trimetallic nanoparticles is particularly important for their application. However, these properties cannot be understood purely from experimental data, due to the small scales and complex structures of bimetallic clusters. Thus, it is necessary to simultaneously use molecular simulation method to investigate them.In this work, the surface segregation phenomena of Au-Pd bimetallic clusters upon CO and O adsorption are investigated by using Monte Carlo simulation. The Johnson’s embedded atom method (EAM) is used to model the metal-metal interaction and the metal-adsorbate interaction potential is developed by the first-principle calculations in the framework of DFT. It is found that the adsorption of CO and O on the Au-Pd bimetallic clusters can greatly change the surface segregation of Au in the free cluster into the surface segregation of Pd, which is even completely reversed at the high CO and O coverage close tolmonolayer.Furthermore, the thermal properties of the crown-jewel (CJ) structured Au-Pd nanoalloys with atoms from561to2057are studied by molecular dynamics simulations, based on the Gupta potential. The effects of composition and size on the melting of the CJ structured Au-Pd nanoalloys are discussed. It is found that doping of Au atoms on the Pd clusters could decrease the thermal stability of the Pd cluster, where the melting point of the cluster decreases with the concentration of the Au atoms. It is also found that the melting point of the cluster is associated with a linear decrease with the inverse cluster diameter for the five types of the clusters, corresponding to the Pawlow’s law.Monte Carlo and Molecular dynamics simulations were used to investigate the cluster-size and composition effects on the Structures and melting behavior of icosahedra structured(fcc before melting W4≈-0.16) Au-Pd-Pt clusters with atoms from55to561, based on the Gupta potential. It is found the Segregation Phenomena of Au atoms systematically are segregated on the surface of the Au-Pd-Pt cluster, and the Pt and Pd atoms are enriched on the inner shell. Furthermore, the lowest value of△564Gup achieved for Au-Pd-Pt cluster, indicating that the composition of NP-5(1:2:2) is relatively stable at the Gupta level among these clusters.