Al$_{n}$Bi Clusters: A Transition from Aromatic to Jellium Stability

Through a synergetic effort using density functional theory and negative ion photodetachment studies we have investigated multiple aluminum-bismuth clusters. Our studies show that Al$_{3}$Bi and Al$_{5}$Bi are two very stable clusters. Further investigation of their electronic structure reveal that their stability can be explained using the aromatic and Jellium models, respectively. The Al$_{3}$Bi cluster has a large ionization potential of 7.1 eV, a low electron affinity of 1.4 eV and a HOMO-LUMO gap of 1.7 eV. The molecular orbitals of the cluster are reminiscent of an aromatic system and the cluster has a nucleus independent chemical shift (NICS) value of -32.19 ppm confirming its aromatic character. The Al$_{5}$Bi cluster has a HOMO-LUMO gap of 1.2 eV and a large ionization potential of 6.5 eV. The compact structure of Al$_{5}$Bi has 20 electrons, which indicates that this cluster's stability could be accounted for by the Jellium model.