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Using the analytic modified EAM potentials, the surface concentrations and concentration depth profiles of (111) and (10 0) faces of Pt-Pd and Pt-Ir binary alloys are studied with Monte Carlo simulation based on the grand canonical ensemble statistical rule. In Pt-Pd alloy, the topmost surface is enriched with Pd, and the subsurface layer is depleted of Pd. The simulation results show a damped oscillation of Pd concentration in the whole composition range. A strong Pd segregation is observed for both the orientation faces, while the amount of Pd segregation in the (I 11) face is significantly less than that in the more open (10 0) face. However, Pt segregates to the surface strongly in the Pt-Ir alloy, and the amount of Pt segregation in the (10 0) and (I 11) face is almost the same. The simulation results are in good agreement with the available experiment data and other theoretical values. (C) 2002 Elsevier Science B.V. All rights reserved.