Self-consistent linear-muffin-tin-orbitals coherent-potential technique for bulk and surface calculations: Cu-Ni, Ag-Pd, and Au-Pt random alloys

We present an efficient technique for calculating surface properties of random alloys based on the coherent-potential approximation within a tight-binding linear-muffin-tin-orbitals basis. The technique has been applied in the calculation of bulk thermodynamic properties as well as (001) surface energies and work functions for three fcc-based alloys (Cu-Ni, Ag-Pd, and Au-Pt) over the complete concentration range.

The calculated mixing enthalpies for the Ag-Pd and Au-Pt systems agrees with experimental values, and the calculated concentration dependence of the lattice parameters agrees with experiment for all three systems. We find that the calculated surface energies and work functions in the unsegregated case exhibit a small positive deviation from a linear concentration dependence.

Finally, we performed a segregation analysis based on the calculated surface energies by means of a simple thermodynamic model and found in complete agreement with experiment that the noble metals segregate strongly towards the surface of their alloys.