DFT Study Of The Properties Of Small Metal Clusters & Preparation And Research Of Metal Nanoclusters

There are two parts in this theme. Part one includes the DFT studies of the equilibrium geometry, energy, relative stability, electronic and magnetic properties of the noble metal clusters including Au_n(n≤14) and Ag_n(n=2-10), the Au_nX_m(n+m=4, X=Cu, Al, Y) small bimetallic clusters, translation metal clusters including Sen, Y. and La_n (n=2-10), and the Sc_nO and Y_nO (n=1-9) cluster monoxides by using the density functional theory (DFT) under different levels, and study the size dependence of the structure and energetic and electronic properties of these clusters. Parts two is about the preparation and researches of thc silver and gold nanoclusters, and characterization of the structures and properties of them, especially the optical absorption spectra.1. DFT study of the properties of small metal clustersThe studies of the geometric structures, electronic properties and interaction of them, and the size dependence of clusters which are how to influence the properties of clusters, are the key way to know the system of cluster materials which have important applications.For the small gold clusters, the structural changes from the planar [two-dimensional (2D)] to the three-dimensional (3D) geometry would affect the properties of the gold cluster. However, the value of n at which non-planar structures begin is not still determined. In this present work, a systematic study on the structure and electronic properties of Au_n (n≤14) has been performed by DFT based at a GGA level with PW91 functional combined with the LANL2DZ effective core basis set. The properties of gold clusters are directly related to their sizes and structures, so we focus here on small Au clusters with up to fourteen atoms, in order to understand their electronic characteristics as a function of cluster size. In addition, the maximum hardness principle (MHP) proposed by Pearson and the minimum polarizability principle (MPP) are used to discuss stabilities of the small Au small clusters and their chemical reactivities.Several functionals combined with different basis sets for the Au₂ cluster have been examined and compared with previous theoretical and experimental work to conclude that the PW91/LANL2DZ method is the best choice for study of small gold clusters. The turnover point from 2D to 3D for Au clusters occurred at the size of 12 atoms, which is much larger than in copper and silver clusters, owing to the strong relativistic effects and the strong hybridization of the gold atomic 5d and 6s orbitals. The properties of gold clusters are strongly size and structure dependent. The values CN, R_ave of structure properties and E_b, E_b/n of energetic properties for the lowest-energy gold clusters increase monotonically with cluster size. Furthermore, for Au_n (n≥5) especially, E_b/n exhibits an odd-even effect which has relative higher binding energy with clusters having even numbers of atoms than neighboring clusters having odd numbers of atoms. The parameters D(n, n-1) andΔ₂E(n) exhibit obvious even-odd oscillating behaviors on increasing cluster size. The relative stability implies that the clusters with even numbers of atoms arc more stable than those with odd-numbers of atoms. There is no obvious relationship between the HOMO-LUMO energy gap and cluster size. However, some clusters with even numbers of atoms still have larger values than their neighbors with odd numbers of atoms. The VIP shows a remarkable odd-even oscillation where the odd-numbered clusters have higher VIP than the even-numbered clusters. However, the EA have an opposite alternation patterns compared with the VIP. Chemical hardness and static polarizability also exhibit even-odd oscillating behavior. The more stable clusters having larger chernical hardness and less static polarizability are in agreement with MHP and MPP, which are operative principles in characterizing thc properties of clusters, respectively.The systematic methods, including geometric optimization, relative stability, electronic properties, and chemical reactivity, presented in this study are very useful for analysis of the theoretical and experimental data and provide insight into more complicated cluster systems. The geometrical structures of ground state and electronic properties Ag_n(n=2-10) clusters have been performed by DFT based at two levels with exchange-correlation functional by PW91 and B3LYP, respectively, and all combined with the LANL2DZ basis set. The turnover point from 2D to 3D for Ag clusters occurred at the size of 7 atoms. Meanwhile, the atomization energies, the energy level distribution, HOMO-LUMO gaps, the electron aftinities and the ionization potentials are calculated and discussed. And the results of our theory are in reasonable agreement with experimental ones. The atomization energies and electron affinities generally increase with increasing cluster size, and have a relation with the stabilization of clusters. The Fermi level, EA values and VIP values have strongly property of even-odd oscillation with the size of clusters. The law of electronic properties are strongly dependent on the structure of clusters and change with the size of clusters can be used to determine the low-lying structures, and also can explain the results of experiment. In addition, we compared the difference of the VIP and EA by using the PW91 and B3LYP functionals and the experiment data. The MHP and MPP are also used to discuss stabilities of the small Ag clusters and their chemical reactivities.The static mean polarizabilities and polarizability anisotropies of Cu_n, Ag_n and Au_n (n=2-10) clusters have been calculated by the PW91 density functional method. The calculated results are compared with experimental polarizabilities of sodium clusters. It is shown that the size dependency of the static polarizabilities per atom of Cu_n, and Ag_n clusters possesses the same trend as that observed in sodium clusters exception of the Au, clusters which the polarizability is different owing to the strong relativistic effects and the strong hybridization of the gold atomic 5d and 6s orbitals. However, the absolute polarizabilities of the noble-mental clusters are considerably smaller than those of the sodium clusters and the electronic structures of the noble-mental are much more compact.The equilibrium geometries and electronic structure properties of mixed Au_nX_m(n+m=4; X=Cu, Al, Y) have been obtained by using the B3LYP hybrid which based on DFT. The binding energies, ionization potential, electron affinity, HOMO and LUMO energy level, and the energy gaps of them have been calculated. By analyzing the properties of electrons with use of Mulliken population method, it is concluded that impurity increases the stabilities of Au cluster. When Cu, Al and Y doped in Au₄ cluster, the energy gaps reduce and the binding energies increase. The electronic structure of Cu_nAu_m(n+m=4) crystalloid clusters were calculated using density functional theory method of the first principles. It is shown that crystal lattice parameters are in accord with the result of experiment. Through studying the band structure and density of states (DOS), the d orbit electrons support for the energy levels mainly. And there are strong peak values near the Fermi level of 2eV, the fimction of light absorb will evidently increase over here. The distribution of charge density shows that the bands' densities are very big. And also conclude there are covalence bonds and metal bonds on the studied system, and the metal bonds also come from the communized movements mainly.Several functionals combined with different basis sets for the Sc₂, Y₂ and La₂ cluster have been examined and compared with previous theoretical and experimental work to conclude that the BP86/CEP121G method for small Sc and Y clusters, PBE1PBE/LANL2DZ method for La clusters are the best choice for study their properties. We study the structures, stability, electronic and magnetic properties of the X_n(X=Sc,Y,La,n=2-10) clusters, and these properties change trend dependent of the clusters size. The results indicate that the binding energies per atom increase with the cluster size increases, but there are local maxim at n=4,7,9, and the second differences in total cluster energy also prove of them have relative high stability, the same group clusters have the same results. The energy gap of La cluster are higher than Sc and Y clusters, and the high energy gap are found at n=4, 7, 9 clusters. The value of VIP and EA have not odd-even oscillation which like the Au and Ag clusters, the EA of Sc clusters is higher than Y and La clusters', but the change trends are the same for them. The static polarizability of La cluster is lover than the Sc and Y clusters'; and there are also have local minimum at n=4, 7, 9 with the cluster size increasing. The small X_n clusters exhibit big and anomalous magnetic moments; there is a remarkably good agreement between the calculated value and experiments. The magnetic moments are mainly dependence on the symmetry, atomic coordination number and the distance of clusters. The average magnetic moments of three clusters are all decrease with the clusters' size and there is local oscillation character. The size dependence of average magnetic moments can be explained by the model with geometry dense gather.Several functionals combined with different basis sets for the ScO and YO cluster have been examined and compared with previous theoretical and experimental work to conclude that the the best choice is BP86/CEP121G method for study the small Sc_nO and Y_nO clusters. The state and geometry of the low-energy structures have some difference for Sc_nO and Y_nO dusters. The average binding energy of Y_nO clusters is higher than which of Sc_nO clusters and XO-X₅O clusters decrease with the size of clusters because of the stronger bonding, and there is an odd-even oscillation with the cluster size increasing for X₄0 to X₉O clusters. The second differences in total cluster energy also prove of even-numbered Sc or Y atom of the clusters monoxides has relative high stability. There are no obvious trends of the energy gap, but there are higher gap for those of stable clusters. There is a remarkably good agreement between the calculated value and experiments for the calculated value of VIP and EA. The VIP decreases with the cluster size increasing for both of Sc_nO and Y_nO clusters, but the calculated VIP of Y_nO maybe some underestimate compared with experiment data. The calculated EA decreases from ScO to Sc₄O clusters, and alternate increase for the larger clusters (n≥5); but the EA of Y_nO exhibit an obvious odd-even oscillation and increase alternatively as the cluster size increasing. The MPP are used to discuss stabilities of the small Sc_nO and Y_nO clusters by analyzing the calculated average static polarizability.2. Preparation and research of metal nanoclustersNanoclusters is the one of new material that now most gets solicitude, its important meaning is more and more known for people to share. Research and the preparation of nanomaterial are the foundation of nano-ST. As nanotechnology is continuously developed has put forward higher requirement for the preparation of nanopowder: Need to prepare the various, shape look and structure that specifies size, equality the adjustable nanometer pellet, pure and unpolluted to support application and development. The demand of nano-size metal clusters will increase increasingly with technology to develop, especially. This paper with the actual needs of metal physical doping of ICF target material and laser - X-ray conversion material is starting point, major for the preparation method and the technology parameter control panicle grain size of the Ag and Au nanoclusters by flow-levitation technique and magnetron sputtering technique, respectively. And characterize the structure, thermal stability of phase composition and optical absorption spectra for the preparation metal nanoclusters which including go deep into research.Silver nanoclusters have been prepared by flow-levitation technique. The nucleation and growth mechanism of clusters were studied theoretically and the experiment conditions and technological parameters were studied experimentally. The morphologies, granularities, structures, chemical components and electronic structure properties of silver nanoclusters have been characterized. The results indicate that the morphologies of Ag nanoclusters are approximately spherical, the structure of them are face center cubic (FCC), the dispersion is homogeneous, and the particles are pure and unpolluted. The average size and their dimensional distribution of Ag nanoclustcrs mainly depended on the cooling efficiency of inert gas, gas flow velocity, inert gas pressure, temperature and size of metal drop. Only He was utilized as the carrying gas for producing particles with an average size less than 10nm. Optical absorption spectra of Ag nanoclusters was studied by theory and experiment, the surface plasmon absorption strongly depend on the size of particles. Because of the quantum size effect, as the particles size decreasing, the plasmon peak shifts toward the short wavelength while the plasmon band width increases.Gold nanopclusters have been prepared by magnetron sputtering technique, and their morphologies, granularities, structures; optical absorption properties and chemical components have been characterized using TEM, XRD, UV-Vis and XPS. The results indicate that the morphologies of gold nanoparticlcs are approximately spherical, the average size is estimated to be about 10nm, and they are pure and unpolluted. The stricture of gold nanoparticles is face center cubic (FCC). The surface plasma resonant absorption appears at 519nm.The binding energy of 4f_7/2 and 4f_5/2 electrons of elemental gold atoms arc 83.3ev and 86.9ev, respectively, and here is no asymmetry in he peak shape to indicate that all the Au atoms are in their zero oxidation state.