Surface effects on structural and thermodynamic properties of Cu3Au nanoclusters

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. Cu3Au 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 Cu3Au and the surface gold segregation is a continuously decreasing function of temperature, irrespective of the first order–disorder phase transition in the cluster. # 2003 Elsevier B.V. All rights reserved