Structure and electronic property of medium-sized silicon clusters

The lowest energy structures of Sin   (n=10–20n=10–20) clusters are obtained using the first principles pseudopotential simulated annealing within the local density functional approximation (LDA) implemented in SIESTA method. New low-energy structures are obtained for each cluster size. The Sin   clusters generally follow a prolate structures for n<16n<16 and, like spherical structures, with the appearance of an endohedral atom with highly co-ordination starting at n⩾17n⩾17. The size dependence of clusters binding energies, and highest-occupied and lowest-unoccupied molecular orbital (HOMO–LUMO) gap are discussed.