Theory Study On The Structures And Properties Of Sn And Pb Clusters Doped With Transition-Metal Atoms

One of the major objectives of cluster science is to discover stable atomic clusters, which may be used as building blocks for cluster-assembled materials. On the other hand, density functional theory (DFT) is an important research method for condensed matter physics, quantum chemistry and materials science based on the combination of quantum mechanics and chemistry as well as development of theory and numerical algorithm. In this dissertation, the geometric, electronic, optical, and magnetic properties of the 3d transition-metal-doped clusters of Sn and Pb are studied, using the density-functional method.In the first chapter, we review the developments of the nanometerials of the Group 14 elements, including fullerene, Carbon nanotube, clusters of silicon and germanium, nanotubes of silicon and germanium, and the clusters of tin and lead.In chapter 2, we introduce the development of the quantum chemistry as well as the basic concept of DFT and review its recent progress. To effectively introduce DFT, we start with the basic theory to find the appropriate exchange and correlation energy functional as the main line. Finnally, we list some popular program packages in the dissertation in detail.In chapter 3, we focus on the geometric, electronic, optical, and magnetic properties of the 3d transition-metal-doped clusters of Sn. First, we study the geometric, optical, and magnetic properties of the M@Sn12 clusters (M=Ti, V, Cr, Mn, Fe, Co, Ni). The geometric optimization shows that the ground states of these clusters are probably very close to the Ih structure. Our calculations demonstrate that the magnetic moments of them vary from 2?B to 5?B by doping different d transition-metal atoms into Sn12 cage, suggesting that M@Sn12 could be a new class of potential nanomaterials with tunable magnetic properties. Second, for Ni2Sn17, Mn2Sn17, [Ni2Sn17]4-and [Mn2Sn17]2-, three probable geometries with D2d, D4d, and D4h symmetry are considered as the starting configurations. It was found that the D2d structures of these clusters are the most stable structures among the three possible isomers. Finally, we study the geometric and magnetic properties of the Mnx Sny clusters (x=2,3,4; y =18,24,30). The geometric optimization indicates the MnxSn6x+6 clusters (x=2,3,4) are favorable to form Mn atoms endohedral Snn cage structure, namely, Mn2@Sn18, Mn3@Sn24, and Mn4@Sn3o, while the MnxSn6x+12 clusters (x=2,3) prefer to form structures based on two small clusters, namely, Mn@Sn12-Mn@Sn12 and Mn@Sn12-Mn2@Sn18. Thus, MnxSny is possible to form different 1D nanowires by the different number of Mn dopant. In chapter 4, we pay our attention to the geometric, electronic, and magnetic properties of the 3d transition-metal-doped clusters of Pb. First, the geometric and magnetic properties of the MPb10 clusters and their dimers (M=Fe, Co, Ni) are studied. The calculated results show that the structure of MPb10 with an encapsulated square antiprism geometry is energetically favorable. These clusters could form a stable dimer cluster and retain their structural identity. The most stable structure of the [MPb10]2 is the two MPb10 monomers to be bonded at the triangular faces which are facing upside down with respect to each other. Owing to the large doping energy of NiPb10 and small interaction energy of [NiPb10]2, NiPb10 would be a good candidate as the building block for cluster assembly. The magnetism calculations reveal that the dimerization does not lead to the substantial changes of the local magnetic moments of Fe atoms and the magnetic order between Fe and Pb atoms, while it can affect the local magnetic moments of Co (or Ni) atoms and the magnetic order between Co (or Ni) and Pb atoms. Second, the geometric and magnetic properties of the M@Pb12 clusters (M =Sc, Ti, V, Cr, Mn, Fe, Co, Ni) are studied. The geometric optimization shows that the ground states of these clusters are close to the Ih, structure. The magnetic moments of M@Pb12 vary from 1?B to 5?B by doping different transition-metal atoms into Pb12 cage. The electronic structure calculation shows that the Mn@Pb12 has large energy gap and doping energy, and its structure and energy gap remain unchanged with a strong external electric field up to 0.1 V/A, thus, Mn@Pb12 would be a good candidate as the building block with high magnetic moment for cluster assembly.