Bond order simulation model: Coordination dependent bimetallic bonds

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Abstract
The variation of metal–metal bond strength or atomic site energy with number and type of atomic neighbors is described within a generalization of the bond order simulation (BOS) model, named the BOS‐mixing model. The site energy for fixed coordination is expressed as a quadratic function of the number of existing mixed metal bonds. The three parameters in this functional form are (over)determined by the mixing energy as a function of composition for bulk bimetallic fcc systems. For the ten bimetallic alloys formed from Ni, Cu, Rh, Pd, and Ag, we find that the BOS‐mixing model describes the composition dependence predicted by non‐self‐consistent electron density functional theory. Using the same BOS‐mixing parameters obtained from this non‐self‐consistent electron density functional theory, the BOS‐mixing model predicts accurately the microstructures (coordination arrangements) of clusters of Ni101Cu100, and Cu101Pd100 which are prototypical systems for bimetallic clusters. For Ni101Pd100 the BOS‐mixing model displays some inaccuracies due to the atomic size mismatch of 10% which distorts the cluster shape from a perfect lattice structure. This is the same effect noted in previous applications of the BOS model and is thus expected.

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