3.2.2 Electronic Properties
The stability of clusters can also be evaluated by certain electronic structure related descriptors including vertical ionization potential (VIP ), vertical electron affinity (VEA ), chemical hardness, the highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, and polarizability, etc. VIP is the energy difference between the ground state of the neutral cluster and the ionized cluster that has the same geometry as the neutral. In this work, the VIP s of the lowest-energy structures of AlBen were calculated at the B3LYP and CCSD(T) levels. From the results shown in Figure S1a, the two curves show generally consistent trends. Either curve has two striking peaks atn = 2 and 8, implying that the AlBe2 and AlBe8 clusters are not apt to lose an electron. Meanwhile, the CCSD(T) results of AlBen and Ben +1 clusters are compared in Table 2. From the table, the VIP value of AlBen is always smaller than that of its corresponding Ben +1cluster except for n = 6.
Table 2. Vertical Ionization Potential (VIP , in eV), Vertical Electron Affinity (VEA , in eV), and Hardness (η , in eV) of the Lowest-energy Ben +1 and AlBen (n = 1–12) Clusters at the CCSD(T)// B3LYP/aug-cc-pVDZ Level.