Density Functional Theory Study of Structural Evolution, Relative Stability, and Electronic Properties of Sn_nAl_n (n =2-12) Clusters

The ground-state structure, average binding energy (E-b), fragmentation energies (Delta E), second-order difference energy (Delta E-2), gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), vertical ionization potential (VIP), vertical electron affinity (VEA), and charge transfer of SnnAln (n = 2-12) clusters are evaluated by density functional theory (DFT). With an increase in the cluster size n, Al atoms aggregate in the geometric center of the cluster, and Sn atoms encapsulate Al atoms in the periphery of the cluster. The variation of Delta E, Delta E-2, the HOMO-LUMO gap, VIP, and VEA of the SnnAln clusters follows similar trends, with certain odd-even oscillations. However, beyond the cluster size n >= 9, the HOMO-LUMO gap decreases significantly, and the VIP and VEA fluctuate significantly, indicating a deterioration of the relative stability of the cluster. Charge transfer proceeds from the Sn atom to the Al atom. This study provides an analysis of the interaction between Sn and Al at the atomic level and explains the segregation phenomenon during the preparation of tin-aluminum alloys.