N-doped Effect On M Clusters (m=fe, Co, Ni) And Theoretical Investigation For Structure Evolution Of Gold Clusters

Clusters have been paid more attention due to the unique geometric structures and novel properties. With the development of the density functional theory (DFT) in the recent years, DFT calculations based on the first principle have been already applied in the condensed matter and computational chemistry. In this dissertation, DFT calculations have been performed on the N-doped transitional-metal magnetic clusters and the special-sized gold clusters.In Chapter one, we firstly outline the research progress on the transitional-metal clusters and the gold clusters. At the same time, we give the research objects in this dissertation. In Chapter two, we briefly introduce the density functional theory and the computational programs used in the dissertation.In Chapter three, we investigate the effect of N-doping on the configurations and magnetic properties for MnN clusters (M = Fe, Co, Ni; n = 2–12, 14, 18). The results are as follows: 1) On doping an N atom into the pure Mn clusters, the binding energies of the resulting mixed clusters have increased as cluster size n becomes large with 1≤n≤10. While n exceeds 10, there exists the gentle tendency. In compare with the pure Mn clusters, the doping of N atom enhances the stability of clusters. 2) The N atom doped in the clusters prefers the surface sites except for n = 14 and 18. 3) According to the Mülliken analyse, the Mülliken charges have the tendency transfering from the metal atoms to the N atom; the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital display the dependence for the cluster size n. Moreover, due to the doping of the N atom, the total spin magnetic moments of all the M atoms decrease for most of clusters. 4) For some special-sized clusters, FenN (n=9,12,14),ConN (n=8, 9,11,18),NinN(n=3,11,12), the comparement between the surface-enhanced effect and the quantum size effect resulted in the enhancement of the total spin magnetic moments of all the M atoms. Otherwise, quantum cofined effect has resulted in the "quantum terrace" for NinN clusters. In Chapter four,Au18 clusters have been investigated by using the relativistic density functional calculations with the different exchange and correlation functionals. Considering the stronge relativistic effect for gold element, researchers have already predicted the Au32 fullerene with the strong spherical aromaticity. Thus, Au18, as the smallest spherical-aromatic cage and magic clusters according to the jellium model, the studies on its structures and aromaticity attract more attentions. Through our theoretical calculations, we list the main results as follows: 1) Leading candidates for the lowest-lying Au18 clusters are discovered as the hollow cages with the spherical aromaticity. 2) A new D4d tubular isomer with strong spherical aromaticity is theoretical came up with. 3) On the basis of D4d tubular isomer, we develop it into a new class of metastable gold nanotubes.The famous pyramidal Au20 and Ih-symmetry Au32 fullerene have been two noticeable magic clusters so far. The size-dependent evolution of structural and electronic structural motifs for Aun(20≤n≤32) is investigated using density functional theory within the general gradient approximation. The results are listed as follows: 1) When cluster size n adopts 20, 21, 22, 23 and 26, the lowest-lying structures prefer to the pramidal motif. 2) When cluster size n is 25, a new very promising groundstate candidate is adopted---double-layered motif. 3) At n=27–28, the hollow columnar structures with a single additional atom on the axis appear instead of the transitional hollow tubelike configurations; moreover, for Au28 clusters, there exists a Morse cage as a stronge candinate for the lowest-energy structure. 4) The most-stable structures over the range n=29–32 are obtained by"dualization"procedure from carbon fullerenes.In Chapter six, the cage-like structures for Aun(n=29-35) clusters and Eu@Aun (n=29-35) clusters are investigated using density functional theory calculations. The calculation results give the lowest-energy cage-like configurations and the corresponding properties of Eu@Aun (n=29-35) clusters so as to supply some theoretic referrences for the experiment studies.