First Principles Study Of Silicon Clusters Of Gold

Now nanomaterials are one of the hottest research topics in the field of materials and attract great interest for their special physical and chemical properties. The change of the clusters as the scale varies could reflect the growing process and trend of the materials, which is very important for the self-assembly of nanomaterials.In the paper, the structures and electronic properties of the SiAun (n=17—20) clusters are systematically investigated by using DFT calculations. The most stable structures are got and the NBO bond order, adsorption energies, HOMO-LUMO gaps, absorption spectra and IR spectra are investigated. The results are as follows:doping with silicon could significantly change the structures of the gold clusters. For the SiAun (n=17—20) clusters, the SiAun17,18,20exhibit shell-like cage structures with an Au atom dangling on top of Si which is embedded on the cage surface, much different from pure Au clusters. The dopant Si atom with the neighboring Au atoms forms a SiAu5,6unit. The SiAu19cluster prefers a tetrahedron-like structure with a dangling Au atom, where the dangling Au atom on Si forms Au-Au bonds with other two neighboring Au atoms. The SiAu2o has a calculated gap of about1.0eV which may be a good candidate for biomedicine. By the population analysis, we find that the gold atoms around the cage carry positive charges and the others have negative or no charges. The IR spectra have much relationship to the structures, and these characteristic peaks may be used as a signature for experimental identification of the configuration.The electronic structure and optical properties of the Au (111) surface doped with a Si atom are studied using the first-principle calculations. The best adsorption location and the transport barrier among the locations are researched. The PDOS, different charge density, Mulliken charge and bond order, absorption spectra and IR spectra are also indicated. The results show that the Si atom binds with six Au atoms when it is doped in the bulk; and the p-orbital electrons are more localized. While the barrier is lower than others when Si transports on the surface. By analyzing the electron density difference, we find that the electron densities at the Au atoms surrounding the Si atom are relatively smaller, while those between the Au and Si atoms are larger, suggesting the charge transfers from the Au atoms to the Si-Au bonds. The Mulliken bond order shows that the Si atom can form covalent bond with the Au atom, and the surface Si-Au bond order is larger compared with that in bulk. In addition, the calculation of the absorption spectra shows that the absorption intensity is obviously enhanced when the Si atom is doped in the bulk.