First-Principles Study Of The Structural And Electronic Properties For The Small Metal Clusters And Diluted Magnetic Semiconductors

In this thesis, using the first-principles (ab initio) calculation methods based on Density-Functional Theory (DFT), we investigate the total local moments and the electronic properties inside the Muttin-Tin (MT) spheres of zinc-blende ferromagnetic Ga_1-xMn_xAs , Ga_1-xMn_xN and Cd_1-xMn_xTe (x=1.0,0.25,0.0625) Mn-doped diluted semiconductor , and discuss the geometric, electronic, bonding properties and the adsorption and reaction of the small metal clusters, the main contents are presented as the followings:The first chapter is divided into three sections. In the first section, we briefly introduce some basic principles and related current progresses of DFT. The second and the third sections discuss the theoretical foundations and key characteristicses of LAPW ( linearized augmented plane wave ) and DMol³ ( local density functional calculations on motecules ) package used in this thesis in detail.In the second chapter, we calculate the atom and angular momentum resolved Mn-induced local moments in diluted GaMnAs, GaMnN, and CdMnTe semiconductors. We show that the local moments are correlated with magnetic stability and can be explained by the occupation and hybridization of the host states with Mn 3d states in both spin channels. We also show that the splitting of the localized core orbitals follows the sign of the local magnetic moments, but for the delocalized valence states the splitting is determined by hybridization with Mn states. We propose that spin-polarized photoemission measurement of the shallow core states could be used to measure the local moments of the host elements.In the third chapter, we have studied the atomic structures and electronic properties of Al₇I_N (N=1,2,3) and Al₁₃I clusters. The ground state structures of the neutral and charged Al₇I_N(N=1,2,3) and Al₁₃I clusters are obtained. The Mulliken occupation analysis, the distribution of the total charge density difference and the charge distribution of HOMO for Al₁₃I^- and Al₇I₃^- clusters indicate that both of the two clusters have similar behavior. While the negative charge on these clusters, the net charge density distributed around on both aluminum atoms and iodine atom. It is show that we cann't conclude Al₁₃ or Al₇I₂ clusters have the superhalogen properties based only on the charge distribution of HOMO on them. The distribution of HOMO density of Al₁₃I^- and Al₇I₃^- clusters does not necessarily mean that the distribution of net charge on the clusters is also around the aluminum atoms, and the ability of capture electrons of Al₁₃ or Al₇I₂ clusters isn't stronger than that of halogen atom.In the fourth chapter, we discuss the structural and electronic properties of T M₃H_2m (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, m = 1,2,3) clusters. There are strong hy-bridization of the TM 3d states with the H 1s states via the TM As states in all TM₃H_2m clusters. The Mulliken occupation analysis indicates that the negative charge has been transferred from the TM atom to the hydrogen atom. There is strong repulsion interaction between two hydrogen atoms in the hydrogen moleculer, because both hydrogen atoms have the same net charge donated by TM atoms, resulting in the broken of the H-H bond, i.e. the hydrogen molecular is decomposed and adsorbed on TM₃ clusters, which is considered as a catalytic effect of TM atoms for hydrogen storage in the metals and alloys. It is pointed out that the most active additions are (in the order of activity) Ti, V, Fe, Mn, Ni.