Structural, Electronic And Magnetic Properties Of Binary Alloy Clusters For Density Functional Theory Studies

The clusters have attracted extensively attention in condensed matter physical field in virtue of its unique scientific importance and promising applications in catalytic industry, biomedicine, optical communication, microelectronic device and so on. With the discovery of various characters in single component clusters, the focus shifted to the study of binary alloy clusters. Compared with single component clusters, the tunable physical properties with our desired purposes can be obtained in these clusters. Furthermore, the interaction between two elements can result in many particular properties that don’t display in single elementary clusters. Therefore, the comprehensive investigation for binary alloy clusters is very necessary and important, which can help to further understand the generated mechanisms of their characters, and is also the basis of exploiting new functional nanomaterials. The geometrical evolution, electronic structure, and magnetism of Au-Pt and Ho-Si binary alloy clusters are studied in this thesis. The main contents and conclusions are summarized as follows.1. Theoretical study of geometrical evolution and electronic structure of Au-Pt binary clusters.The density functional theory (DFT) with a generalized gradient approximation (GGA) and DFT semi-core pseudopotential (DSPP) is adopted to investigate the geometric, electronic, and magnetic properties of Aun-xPtx (n=2-14, x=0-n) binary clusters. The results show that the most stable structures of the clusters are remain segregated cases in which the doped Ptx components occupy central positions and surrounded by host Aun-x components. Generally, the planar structures are observed for small Aun-xPtx clusters and Au-rich clusters up to n=13, while the3D configurations are favorable for Pt-rich clusters with ri≥1and all different constituent Aun-Ptx clusters starting from n=14. The detail calculations of the average binding energies, second order energy differences, and fragmentation energies indicate that the Au6Pt clusters is the most stable in monoatomic Pt-doped Aun-1Pt clusters, and the relative stabilities of AUn-xPtx clusters escalate gradually with increasing of substitutional Pt atoms. Moreover, the obtained highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gaps, electron affinities, and total magnetic moments exhibit obvious odd-even alternations for Aun-1Pt clusters, suggesting that the Pt atom barely influences the electronic structures of these clusters.2. Density functional study of the structural and magnetic properties of HoSin, alloy clusters.The geometrical and electronic structures as well as magnetism of HoSin (n=1-12,16, and18) clusters are studied based on the DFT within the framework of GGA. The geometrical evolution of HoSin clusters is found to be similar to that of other lanthanum (Ln) element doped Si clusters, the Ho atom in the most stable structure gradually moves from surface to interior site as the number of Si atom varies from1to18. Furthermore, starting from n=18, the Ho atom in HoSi18clusters completely drops into the center of Si frame and forms the Ho-encapsulated fullerene cage. The relative stabilities of HoSin clusters increase along with the number of Si atoms n. According to the second order differences of energies, one can observe that the HoSin clusters with n=5,8, and10are more stable than their neighboring sizes. Compared with the bare Si clusters, the doped Ho atom decreases the HOMO-LUMO gaps of HoSin clusters. The analysis of atomic charge indicates that the direction of charge transfer between Si and Ho atoms reverses and the amount of charge transferred from Si atoms to Ho atom obviously increases at n=18. The total magnetic moments of HoSin clusters are3μB, and they don’t quench even the Ho atom enclosed in Si cage framework.