Optimally stuffed fullerene structures of silicon nanoclusters

The stuffed fullerene structures of nanoscale silicon clusters have been studied using density functional theory. Taking Si₄₀ as a prototype, stuffed fullerene cages with a different ``stuffing/cage'' ratio (i.e., Si₄@Si₃₆, Si₆@Si₃₄, and Si₈@Si₃₂) and topological structures have been constructed with the aid of local optimization by simulated annealing with tight-binding molecular dynamics. DFT minimization of these ``handmade'' structures show that the Si₆@Si₃₄ is the optimally stuffed cage with lowest energy, in agreement with previous unbiased genetic algorithm optimization with tight-binding method. The optimal ratio between the number of atoms on the fullerene cage and that stuffed inside can be understood by the effect of space filling. The binding energy and electronic properties of Si₄₀ cluster is calculated and compared with available experiments.