Local-environment fluctuations and densities of states in substitutionally disordered alloys

We report calculations of densities of states (DOS) associated with specific atomic configurations of compact clusters in substitutionally disordered alloys describable by a Hamiltonian with nonoverlapping muffin-tin potentials. The method of calculation consists in evaluating the Green function associated with a cluster of atoms embedded in a translationally invariant effective medium such as the one determined in the Korringa-Kohn-Rostoker, coherent-potential-approximation (KKR-CPA) method. This method yields well-defined, analytic, and physically meaningful results and takes proper account of the crystal structure of the lattice. Numerical results are reported for near-neighbor clusters in both one-dimensional model muffin-tin alloys, as well as in realistic ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}$ alloys. The DOS associated with many cluster configurations exhibit more structure than the DOS calculated in the single-site KKR-CPA method, which can be understood in terms of fundamental physical quantities, such as the relative scattering strength of the alloy constituents, and of the symmetry of the lattice. Several possible applications of cluster DOS in calculating the physical properties of substitutionally disordered alloys are discussed.