NinAlm alloy clusters: analysis of structural forms and their energy ordering

Structural forms of model NinAlm,n + m = 13, alloy clusters are studied for all stoichiometric compositions using a many-body potential. These forms are distinguished by their geometries (isomers) and the distributions of the two types of atoms within a given geometry (homotops). General notions of mixing energy and mixing coefficient applicable to arbitrary, including many-body, potentials are introduced. It is shown that for each stoichiometry the energy ordering of the homotops, within classes defined by the isomeric form and the type of the central atom, is governed by the degree of mixing as measured by the mixing coefficient.