Theoretical study in nano-structure-physics of magnetic atom bridges and molecular bridges

本文采用基于密度泛函理论的第一性原理计算方法，研究了磁性原子桥和磁性分子桥的纳米物理性质。在研究了金属表面和STM针尖之间构建的磁性原子桥的稳定性和磁性之后，我们开始研究磁性分子桥，这些分子桥具有高度可重复的结构来支撑磁性原子。我们以过渡金属M为中心金属原子处理带状卟啉，其中M=Sc，Ti，V，Cr，Mn，Fe，Co，Ni和Cu。发现当M= Sc，Ti，V，Cr，Mn和Fe时，体系为铁磁性金属。当M=Co，Ni和Cu时，系统为绝缘体。为了探讨这些带的电子性质的来源，我们还计算了M卟啉分子的相应孤立单元，它们的中位和β-碳被氢原子封端。结果表明，分子轨道在中位碳和β碳上具有电荷分布，在分子间相互连接形成带时成为宽的能带。另外，我们还发现CO分子吸附在Fe带卟啉上时，会发生金属-绝缘体转变。我们阐明了这种金属-绝缘体转变是由Fe的dxz和dyz轨道与CO分子的II^* g轨道杂化引起的。

We investigated the nano-physics of the magnetic atom bridges and molecular bridges with the aid of the first-principles calculations based on the density functional theory. After we researched the stability and magnetic properties of the magnetic atom bridge constructed between metal surface and STM-tip, we started researching the magnetic molecular bridges, which have their highly-reproducible structures supporting the magnetic atoms. We treated the tape-porphyrin with the transition metal atom, M, as a centre metal atom, in which M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. We found that in the case of M= Sc, Ti, V, Cr, Mn and Fe, the systems are the ferromagnetic metals. In the case of M=Co, Ni and Cu, the systems are insulators. In order to investigate the origin of the electronic property of these tapes, we also calculated the corresponding isolated unit of M porphyrin molecule, whose meso-and β-carbons are terminated by hydrogen atoms. As the results, The molecular orbital, which has the charge distribution on the meso-and β-carbons, becomes the wide energy bands when the molecules connect each other and construct the tape. So in the case where their Eigen energies lie near the Fermi energy, the corresponding tape-porphyrin is conductor.In addition, we found that the metal-insulator transition occurs when a CO molecule adsorbed on the Fe tape-porphyrin. We clarified that such a metal-insulator transition is caused by the hybridization of the dxz and dyz orbitals of Fe with the II^* g orbitals of CO molecule.