Geometric, Electronic, and Optical Properties of a Superatomic Heterodimer and Trimer: Sc@Si16-V@Si16 and Sc@Si16-Ti@Si16-V@Si16

The geometric, electronic, and optical properties of a heterodimer and trimer consisting of metal-encapsulating silicon cage clusters, M@Si-16 (M = Sc, Ti, V) with D-4d symmetry, are studied using density functional computations to explore the possibility of using these clusters as building blocks for a nanometer scale heteroassembly. In this study, among the possible low-lying geometries, the linear-form of the hetero-oligomers is adopted as a model system, where the D-4d monomers are covalently bonded by facing their squares in an eclipsed fashion. The heterodimer consisting of halogen-like Sc@Si-16 and alkaline-like V@Si-16 has a dipole moment of 7.63 D, and its occupied and virtual frontier orbitals are localized to V@Si-16 and to Sc@Si-16, respectively. Some of the inner molecular orbitals exhibit superatomic bonding and antibonding character. The electronic excitations involve charge-transfer states mainly from V@Si-16 to Sc@Si-16 in the optical energy region. The linear heterotrimer of Sc@Si-16-Ti@Si-16-V@Si-16, formed by inserting the rare-gas-like Ti@Si-16, has a larger dipole moment of 15.6 D and one or more localized frontier orbitals compared to the dimer. We propose possible formation routes to realize the present hetero-oligomers using photoexcitation or energy-selective electron injection into several LUMOs of the monomers that are suitable for linear-oligomerization.