The preference of synthesis modes and routes of stable Aln+m (n + m ≤ 13) clusters

By using linear synchronous transit (LST) and quadratic synchronous transit (QST) methods, the formation routes of stable Aln (n = 2–13) clusters assembled by two small clusters have been investigated in the framework of first-principles calculation. The addition of one sole atom to a cluster, i.e., the growth process, is generally automatic exothermic reaction, except for the growth of non-crystal configurations on the basis of crystal clusters. For the association of one cluster with another, i.e., the coalescence process, there usually exists reaction energy barrier ΔER-T. Comparison of the reaction heats ΔHR-P and activation energy ΔER-T suggests that the coalescence processes are more favorable than the growth processes for Aln (n = 2–13) clusters. In the coalescence processes, the clusters with typical crystal symmetry elements, i.e., the crystal clusters, have higher formation ability than those with fivefold or tenfold symmetry axes, i.e., the non-crystal clusters. The formation with non-crystal Al7 cluster as a precursor, i.e., Alm + Al7 → Alm+7, is most preferable in energetics among the coalescence routes considered.