Search

The optical absorption spectra of Si2–Si33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ∼12 eV, it is noted that all the clusters have remarkable absorption in deep ultraviolet region of 100–200 nm, and the maximum absorption intensity is ∼100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.

We have performed global structural optimizations for neutral lead clusters Pb(n) (n = 2-20) by using a genetic algorithm (GA) coupled with a tight-binding (TB) potential. The low-energy structures identified from a GA/TB search were further optimized at the DFT-PBE level. The calculated results show that the Pb(n) (14n/= 20) clusters favor compact spherical structures with hexagon and pentagon rings. These structures are different from those of Si(n), Ge(n), and Sn(n) clusters which favor prolates in the same size range. The binding energies, second differences in energy, and fragmentation behaviors of the Pb(n) clusters were also discussed. Pb(n) (n = 4, 7, 10, 13, 15, and 17) clusters are found to be special stable clusters, which is in good agreement with the experimental results.