Plasmonic Resonances in the Al₁₃^– Cluster: Quantification and Origin of Exciton Collectivity

Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of attention for their potential range of applicability. Unlike other metal nanostructures, a wide variety of aluminum nanostructures show very promising plasmonic properties. Theoretical and computational investigations helped to understand the nature of collective excitations in such finite systems. However, such theoretical investigations are based on qualitative approaches rather than accurate quantitative methods. In the present work, the collectivity of the low-lying states of Al 13 – are investigated within the time-dependent density functional theory and analyzed through different computational tools. A novel tool, which provides a quantitative index of the collective nature of the electronic excitations, has been introduced, the so-called transition inverse participation ratio (TIPR) index. The obtained results suggest the presence of plasmonic-like transitions in the Al 13 – cluster and that these transitions are linked to the icosahedral symmetry of the cluster, allowing the rationalization by the simple jellium model. We believe that the present work opens the opportunity for the study and applicability of this type of electronic transition in aluminum clusters and in other related nanostructures.