Density Functional Theory Studies Of Fe And Co Atom Doped B Clusters

Geometric structures, electronic properties and magnetisms of FeB_n(n≤15) and CoB_n(n≤19) clusters have been explored using density functional theory(DFT) methods.In chapter 1, we give a brief introduction to clusters. Firstly, we introduce the basic conception of clusters. We also give a simple introduction of the review of the studies having done on clusters. Secondly, we introduce the category and research meaning of clusters. Then, we simply describe the results and purpose of our work on clusters.In chapter 2, the basic concepts and progress of DFT are introduced. Development of quantum chemistry promotes the establishment of DFT. Thomas-Fermi model is the first theory using density of electrons as the main variable. Theorem of Hohenberg-Kohn is the fundament of DFT and is developed to Kohn-Sham equation, which can be used to perform real calculations. Now, new corrections and extensions, together with developed exchang-correlation functionals, have made DFT more accurate and suitable for more systems. At the end of this chapter, we introduce the Dmol3 and Gaussian software.In chapter 3, the equilibrium structures, electronic properties and magnetisms of FeB_n(n≤15) clusters have been investigated by generalized gradient approximation (GGA) of density functional theory at different spin multiplicities. The average atomic binding energies, second-order energy differences and gaps of the lowest energy structures are calculated and discussed. The results show that FeB₃, FeB₈, FeB₁₂ and FeB₁₄ possess relatively higher stabilities. Moreover, there is a distinct hybridization between the d orbital of Fe and the p orbital of B for the lowest energy structures. The total magnetic moment for the lowest energy structures is mainly provided by 3d orbital of Fe atom, and exhibits the odd-even oscillation tendency with the increasing of cluster size.In chapter 4, the equilibrium structures, electronic properties and magnetisms of CoB_n(n≤19) clusters have been investigated by generalized gradient approximation (GGA) of density functional theory at different spin multiplicities. The lowest energy structures of CoB_n(n≤19) clusters, with the size increasing, have gradually evolved from planar shape to cubic structure and the site of Co transfers from the main clusters' outer surface to inner direction. The second-order energy differences of the lowest energy structures show that CoB₃, CoB₇, CoB₁₀, CoB₁₂, CoB₁₄ and CoB₁₆ clusters possess relatively higher stabilities. The strong hybridization between the d orbital of Fe and the p orbital of B for the lowest energy clusters. For n<13, the Co atom locates in the peripheral position of the main cluster, with positive electrical charges and magnetic moment, whereas with negative ones for n≥13 when the Co atom transfers into the inner part of the cluster and its magnetic moment almost disappears. The total magnetic moment for the lowest energy cluster is mainly provided by 3d orbital of Co atom.