摘要：

The melting processes of different-sized copper nano-clusters supported on graphite (0001) plane are investigated by the molecular dynamics method. In this work, the melting point is predicted through the caloric curve. The simulation results show that the melting point of the supported copper nano-cluster is higher than that of the isolated one with the same Cu atoms. In the heating process, the copper nano-particle will adhere to the (0001) face of graphite with its (111) face. Pair analysis results show that the copper atoms close to the graphite can keep with order arrangement even when the temperature is higher than the melt point of the isolated nano-cluster.Keywords: copper nano-cluster,graphite,molecular dynamics,pair analysis,1. IntroductionMetal nano-clusters have attracted continuous attentions and have been used in a wide range of applications because of their excellent properties. For instance, metal nano-clusters can catalyse reactions of spanning hydrogenations, enantioselective hydrogenations, hydrosilylations, hydropyrolysis, hydrogenolysis, oxidative acetoxylation, etc. Many researchers immobilised the metal nano-clusters on supports for stabilising the catalyst because the nano-catalysts are unstable at ambient conditions. The physical and chemical properties of the nano-clusters on solid surfaces are dependent not only on their particle size and chemical composition, but also on the structure of the surface and the configuration of the metal/substrate interface. Therefore, more effort should be dedicated to understanding the structure and melting behaviour of nano-cluster supported on substrate. However, the melting process of nanomaterial investigated by experiment is very difficult. Fortunately, theoretical simulations can provide an excellent method to study the melting process at an atomic level. To date, the melting process and thermal properties of many kinds of metal nano-material have been studied by the molecular dynamic method. The size-dependent melting mechanism of the isolated nano-particle has been studied by many researchers. Nevertheless, few efforts focused on simulating the melting process of the supported metal nano-clusters with different sizes.Because copper cluster can be used as a catalyst in many oxidation and hydrogenation reactions, the melting processes of copper clusters with different size supported on the graphite are investigated in the present study. Besides determining the melting temperature of copper cluster, this simulation work also clarifies the effect of graphite substrate on the structural evolution of copper cluster during the heating process.2. Computational detailsThe interactions between Cu atoms in the metal cluster are described by the embedded-atom (EAM) potential with a cut-off of 0.495nm parameterised by Adams et al. The Lennard-Jones (LJ) potential provides an adequate description of the Cu–C interaction, and it has been used in other previous studies. The LJ parameters for the Cu–C interaction are taken directly from: ε=33.5meV and σ=2.926. The long attractive tail of LJ potential is smoothly truncated at 2.0σ. In this study, molecular dynamic simulations are performed using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. And Visual Molecular Dynamics (VMD) is used to display the atomic structure of the simulated models.The initial model for MD simulation, as shown in Figure 1, is a copper cluster with face-centered cubic (FCC) structure and it is placed 3 above the graphite (0001) plane. In order to investigate size-dependent melting behaviour, different-sized copper clusters supported on graphite (i.e. six Cu/G models with copper clusters including 664, 1098, 1686, 2456, 4630 and 5324 Cu atoms, respectively) are selected for simulation. In all the models with substrate, the single layer of graphite (123.0 by 122.1) with 5750 carbon atoms is used. The carbon-carbon bond covalent length in the graphite layer is set to 0.1421nm. The graphite layer is kept rigid and constant during simulation because the layer can't deform when

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