Density Functional Theory Study Of Noble Metals Au-doped And Ag-doped Clusters

In the thesis, the stability, geometrical structures, electronic properties of AgGe_n（n=1-17） clustersand Au₁₂M （M=Na, Mg, Al, Si, P, S, Cl） clusters have been investigated with density functional theory（DFT）. The main contents are presented as the followings:In chapter one, the development of cluster science and significance of the research have beenintroduced.In chapter two, we introduce the basic concept and progress of density functional theory （DFT）.In chapter three, the structures, stabilities, electronic properties and vibrational spectra of the AgGe_n（n=1-17） clusters are systematically investigated using the B3LYP LanL2DZ mothed. The results aresummarized as follows:（1） Different growth patterns appear between small-sized （n=1-11） Ag-dopedgermanium clusters and relative larger-sized （n=12-17） Ag-doped germanium clusters．For the most stablestructures of AgGe_n（n=12–17） clusters， the Ag atom would be completely surrounded by Ge atoms toform Ag-encapsulated Ge_ncages．（2） According to the average atomic binding energy, the fragmentationenergy and the second-order difference of the total energy for different sized AgGe_nclusters, it can beconcluded that the doped Ag in the Ge_nclusters improve the stability of germanium clusters. Moreover, wepredict that the magic number of AgGe_n（n=1-17） clusters should be5，10，12and15．（3） The Mullikenpopulation analysis shows the atomic charges always transfers from the Ge_nframe to Ag atom the in theAgGe_n（except n=10） clusters, indicating that the Ag atom acts as an electron acceptor.（4） Infraredintensities and Raman activities show distinct spectra for these clusters, which also reflect the bondingnature and can distinguish the structures of these clusters from experiments.In chapter four, using first-principles investigation with the density functional theory （DFT）, thegeometries and electronic properties of Au₁₂M clusters （M=Na, Mg, Al, Si, P, S, Cl） have beensystematically studied. All the calculated results are summarized as follows:（1） The Au₁₂M （M=Na, Mg, Al）clusters form cage structures with M atom encapsulated into the center while the lowest-energy structuresof Au₁₂M （M=Si, P, S, Cl） are pyramid with M at the apex. The lowest-energy geometries of Au₁₂M (exceptAu₁₂Na and Au₁₂Mg clusters) are different from high symmetry structure of3d,4d and5d transition-metal impurity doped in Au₁₂clusters. It indicates that different impurity atoms play a completely different role indetermining the structures and properties of Au₁₂M clusters.（2） The Au₁₂S cluster with full closed-shellelectrons not only possesses high relative average binding energy and doping energy, but also high VIP andHOMO-LUMO gap, indicating the Au₁₂S cluster is more stable than other Au₁₂M （M=Na, Mg, Al, Si, P,Cl） clusters.（3） It is obtained that charges always transfer from Au atoms to M atom in all Au₁₂M clustersfrom natural population analysis. The NBO and HOMO analysis show that hybridization between the s-dorbitals in Au atoms and the p orbitals of the impurity occurs in Au₁₂M clusters.