Surface effects on structural and thermodynamic properties of Cu_3Au nanoclusters

摘要

Semi-empirical potentials used for atomic scale modeling in metals are not designed for modeling low coordinance interactions. A popular second moment tights binding potential is revisited and modified for low coordinance systems. Cu_3Au nanoclusters containing no more than a few hundred atoms are used as a case study. The parameterization of this potential is improved and a coordinance correction is presented, based on available experimental and ab initio data for reduced coordinance systems. It is found that a fine tuning of the parameters for bulk materials allows a significantly better description of the order-disorder transition, as predicted by Metropolis Monte Carlo simulations. Short range order does not vanish at high temperature. Accounting for a coordinance correction does not conclusively affect the structural and thermodynamic properties of the cluster cores. At equilibrium, cluster cores display the same stoichiometry as bulk Cu_3Au and the surface gold segregation is a continuously decreasing function of temperature, irrespective of the first order-disorder phase transition in the cluster.