Trends in the formation of aggregates and crystals from M@Si16 clusters: a study from first principle calculations

We have shown recently that the ground state and low-lying energy isomers of the endohedral M@Si 16 clusters ( M = Sc − , Ti, V + ) have a nearly spherical cage-like symmetry with a closed shell electronic structure which conforms them as exceptional stable entities. This is manifested, among other properties, by a large Homo–Lumo gap about 2 eV which suggest the possibility of using these clusters as basic units (superatoms) to construct optoelectronic materials. As a first step in that direction, we have studied in this work, by means of first principles calculations, the trends in the formation of [Ti@Si 16 ] n , [Sc@Si 16 K] n , and [V@Si 16 F] n aggregates as their size increases, going from linear to planar to three dimensional arrangements. The most favorable configurations for n ≥ 2 are those formed from the fullerene-like D 4 d isomer of M@Si 16 , instead of the ground state Frank–Kasper T d structure of the isolated M@Si 16 unit, joined by Si–Si bonds between the Si atoms of the square faces. In all cases the Homo–Lumo gap for the most favorable structure decrease with the size n . Trends for the binding energy, dipole moment, and other electronic properties are also discussed. Several crystal structures constructed from these superatom, supermolecules, and aggregates have been tested and preliminary results are summarily commented.