SURFACE SEGREGATION PROFILE FOR NI50PD50(100)

A recent dynamical LEED study [G.N. Derry, C.B. McVey, P.J. Rous, Surf . Sci. 326 (1995) 59] reported an oscillatory surface segregation prof ile in the Ni50Pd50(100) system with the surface layer enriched by Pd. We have performed ab-initio total-energy calculations for the surface of this alloy system using the coherent potential approximation and o btain an oscillatory segregation profile, in agreement with experiment s. We discuss the energetic origin of the oscillatory segregation prof ile in terms of effective cluster interactions. We include relaxation effects by means of the semi-empirical effective medium theory, and fi nd that this cannot explain the remaining differences between theory a nd experiment. (C) 1997 Elsevier Science B.V.