Theory of segregation using the equivalent-medium approximation and bond-strength modifications at surfaces: Application to fee Pd-X alloys

We have developed, in the framework of a broken-bond model, a method to determine the surface composition of transition metal alloys. The model is based on the equivalent-medium approximation which allows us to calculate the energies of surface layers as a function of local Concentration. The model also considers bond strength modifications at the surface that are determined within a modified tight-binding scheme. The model has been applied to several fee Pd-based alloys. The results are found to be in good agreement with available experimental data.