Revisit of large-gap Si-16 clusters encapsulating group-IV metal atoms (Ti, Zr, Hf)

Doped clusters by Si-16 cage encapsulating group-IV metal atoms (M@Si-16, M = Ti, Zr and Hf) are computationally investigated by both density functional theory (DFT) and high-level CCSD(T) method. Their low-energy structures are globally searched using a genetic algorithm based on DFT. The ground state structures of neutral and anionic M@Si-16 are determined by calculating the vertical and adiabatic detachment energies and comparing them with the experimental data. For neutral Ti@Si-16, the Frank-Kasper (FK) deltahedron with T-d symmetry and distorted FK isomer with C-3v symmetry are nearly degenerate as the ground state and may coexist in laboratory, while the distorted FK isomer is the most probable structure for Ti@Si-16(-) anion. For neutral and anionic Zr@Si-16 and Hf@Si-16 clusters, the ground states at finite temperatures up to 300 K are the fullerene-like D-4d bitruncated square trapezohedron. These theoretical results establish a more complete picture for the most stable structures of M@Si-16 clusters, which possess large gaps and may serve as building blocks for electronic and optoelectronic applications.