The structures, electronic properties, and chemical bonding of binary alloy boron–aluminum clusters series B4Aln0/−/+ (n = 1–5)

Abstract

The geometry structures, electronic properties, and chemical bonding of neutral, anionic and cationic alloy B4Aln (n = 1–5) clusters series were systematically studied by using density functional theory at the B3LYP/6-311+G(d) level of theory for geometry optimization and using coupled cluster single point energy calculations at the CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level of theory. Comprehensive structure search and calculations demonstrate that the Al atoms tend to occupy the periphery sites of all alloy clusters, and the lowest–energy structures prefer low spin states (singlet or doublet). For small alloy cluster with total number of atoms ≤6, the clusters display the rare Anti-Van’t Hoff/Le Bel motifs planar tetracoordinate boron (ptB) and planar pentacoordinate boron (ppB), whereas, for total number of atoms ≥7, it shows 3D configuration. To evaluate the stabilities and electronic properties of the global minimum isomers of each stoichiometry at different charge states, the binding energy, fragmentation energy, second–order difference of the total energy, HOMO–LUMO gap, ionization potential, and electron affinity have been evaluated. We find that for anionic and cationic alloy B4Aln−/+ (n = 1–5) clusters, the odd–n systems are more stable than the even–n ones. AdNDP analyses of the chemical bonding of the global minimum structures indicate that the classical 2c–2e bonds and multicenter nc–2e (n = 3–9) delocalized bonds are responsible for the stability of boron–aluminum mixed alloy clusters.