Theoretical Studies On The Structures, Electronic And Magnetic Properties Of FeAu And FeV Alloy Clusters

Magnetic transition metal?Fe, Co, Ni, Mn? clusters with peculiar physical and chemical properties have attracted many researchers in a variety of related fields. Especially there are in chemical catalysis, magnetic materials, biological, medical and electronics and other fields. A large number of studies on magnetic transition metal clusters present extensive application prospects. More interesting, the binary transition metal clusters can realize that the magnetic properties of clusters have tailing capability and controlled through regulating the size and proportion of the clusters, aiming at obtaining the exotic magnetic properties and being beneficial to produce new type of magnetic nanomaterials. Therefore, the geometries, electronic structures and magnetic researches on transition metal binary clusters have become the focus of research in recent years.In view of this, this thesis chooses the iron-based bimetallic transition metalclusters as the main cluster, which is attributed to Fe clusters have the unique magnetic properties and good catalytic performance. At the same, we select a Au atom with the unique catalytic activity and good bio-compatibility as the doping element in order to explore geometrical, electronic, structures and magnetic properties of Fe Au alloy clusters, promoting that in magnetic storage, catalysis, biology medical and other fields of application. Additional, we select V atom doped Fe₁₃ cluster and carry out a research about a small molecule NO adsorption on Fe_13-nV_n clusters using density functional theory to explore the optimal position of small molecule adsorption and catalytic activity, and finally to provide theoretical guidance for the design of catalysts.The main contents and results are as follows: 1. Structures, stabilities, and magnetic properties of the Fe_nAu ?n=1-12? clustersThe configurations, stabilities, electronic, and magnetic properties of Fe_nAu?n=1-12? clusters have been investigated systematically by using relativistic all-electron density functional theory with generalized gradient approximation. The substitutional effect of Au in Fe_n+1?n=1, 2, 4-5, 10-12? clusters are found in optimized structures which keep the similar frameworks with the most stable Fe_n+1 clusters. And the growth way for Fe_nAu?n=6-9? clusters is that the Au atom occupies a peripheral position of Fen clusters. The peaks appeared at n=6 and 9 for Fe_nAu clusters and at n=5 and 10 for Fe_n+1 clusters on the size dependence of second-order difference of energy, implying these clusters possess relatively higher stability. The analysis of atomic net charge Q indicated that the charge always transfer from Fe to Au atom which causes the Au atom nearly non-magnetic, and the doped Au atom has little effect on the average magnetic moment of Fe atoms in Fe_nAu clusters. Finally, compared with corresponding pure Fe_n+1 clusters, the total magnetic moment is reduced by 3 ?B for most of Fe_nAu clusters except n=3, 11 and 12. 2. Structure, stability, and magnetism of Fe_13-nV_n?n=0-4? alloy clustersDensity functional theory?DFT? for generalized gradient approximation calculations has been applied to study the configurations, stabilities, electronic, and magnetic properties of V-doped Fe₁₃ clusters varying in the range 0 ? n ? 4,Moreover, adsorption of the NO molecules has also been studied to understand the reactivity about V-doped pure Fe₁₃ clusters. As for Fe_13-nV_n?n =0-4? clusters, the lowest-energy structures of all compositions prefer to have icosahedral geometry, in which the central site is always possessed by a V atom and the other V atoms lie on the surface. The number of the surface V atoms and the V-V bonds increases with increasing V doping. Meanwhile, the presence of the V atoms on the cluster surface distorts the cluster geometry. V-doped pure Fe₁₃ clusters are more stable than Fe₁₃ cluster. The total magnetic moments of Fe_13-nV_n?n =0-4? clusters decreases nonmonotonously with the increase of V atoms. NO prefers to adsorp on the top and hollow sites of low-energy Fe_13-nV_n clusters. In addition, the calculated results imply that NO adsorption energies are increasing with the increase of V concentration. Consequently, after adsorption of small NO molecule make total magnetic moments of the main Fe_13-nV_n clusters decreased by 1 or 3 ?B.