Geometry, stability, and properties of Al n (n = 1-13) and Al n Si m (n ? m = 5-7) nanoclusters were investigated by density functional theory. We found that while geometry of some clusters change significantly by substituting of Al atom(s) with Si atom(s) the geometry of some others remain without significant variation. The relative stability of clusters was discussed on the basis of binding energy per atom, fragmentation energy, and second-order difference of cluster energies. Our results

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... al that Al 7 is the most stable cluster among pure clusters. For Al n Si m clusters, it is observed that Al 2 Si 3 (60 % Si), and Al 4 Si 2 (33.33 % Si) are the most stable clusters. The reactivity of Al n and Al n Si m nanoclusters was also investigated on the basis of chemical hardness. The most important feature of chemical hardness is its oscillating behavior as a function of atomic percentage of Si indicating that the reactivity of Al n Si m clusters strongly depends on the composition of cluster.