【作者】 徐辉进；

【导师】 王忠龙；

【作者基本信息】 三峡大学 ， 凝聚态物理， 2011， 硕士

【摘要】 密度泛函理论是研究材料基态物理性质的理论基础,而基于密度泛函理论的第一性原理计算则是研究材料基态性质的强大工具。通过计算,不仅可以解释材料的物理性质,而且可以模拟不同条件下材料的行为。这为预测材料的新性能或者指导新材料的合成提供理论依据。有机化合物要获得宏观的磁性,除了顺磁中心以外,还要求分子具有一定的空间构型,以便顺磁中心的自旋磁矩之间可以相互耦合,因此控制晶体中分子的空间排列情况是设计和合成磁性有机化合物的重要因素。根据这一思路,人们设计和合成了许多金属有机配位化合物。然而,这些研究重点都是放在晶体的结构参数和磁性的关系上面,没有涉及到材料的磁性起源及磁性机理,而了解自旋磁矩的分布对于揭示磁性材料中金属离子通过配位体的耦合机制是不可缺少的。本论文的目的就是利用基于密度泛函理论的第一性原理计算来研究几种配位化合物的电子结构和自旋磁矩分布,以此来揭示化合物中金属离子通过配位体的磁性耦合机制,这对于理解磁性起源与磁性机理有着重要作用。在计算中,我们选用基于全势线性缀加平面波方法的WIEN2k程序,该程序是晶体电子结构计算中最精确的方法之一。首先,我们利用第一性原理方法研究化合物MnCu(pba)(H2O)3·2H2O的电子结构和磁性质。通过计算,发现该化合物存在铜和锰两个磁性中心。铜一桥相互作用显示共价键特征,而锰一桥之间主要是闭壳层相互作用,并且存在强的链内耦合与弱的链间耦合。磁性耦合来源于铜和锰原子向桥联原子的自旋退局域化效应,且具有磁性特征但不具有金属性特征。其次,利用第一性原理方法研究化合物Co(endi)2(N3)2的电子结构和磁性质。通过计算,发现该化合物存在铁磁相互作用,存在强的层内耦合与弱的层间耦合。磁性耦合来源于Co2+向叠氮配体的自旋退局域化效应,且具有半金属磁性的特征。最后,我们还对2,2’-bipyridine配体化合物进行了研究。从[Cu(μ-cbdca)(bpy)]2计算得到的磁矩分布显示,最大的磁矩分布在Cu原子上,并且联吡啶配体呈现少量的磁矩,这说明Cu原子与联吡啶配体之间存在铁磁耦合相互作用,这一铁磁耦合作用来源于Cu原子向联吡啶配体上原子的自旋退局域化效应,但不具有金属磁性。更多还原

【Abstract】 The density function theory gives a firmly theoretical foundation for the study of ground states of materials. The first-principles calculation based on the density function theory has become one of the most powerful tools for the study of ground states in condensed matters. With the first-principles calculation, we can not only get the ground state properties of materials, but also simulate their behaviors under different conditions. This means that we can predict novel properties of materials or design the required materials.To obtain the macromagnetism of organic compounds, the appropriate steric arrange of molecules is important in addition to the paramagnetic centers, for the purpose of the coupling of spin magnetic moments between the paramagnetic centers. So controlling the molecule arrange in the crystals is critical for the design and synthetise of organic magnetic compounds. On the basis of above thinking, a lot of organic-metallic coordination compounds are obtained. However, these researches focus attention on the structure-magnetism relation of crystals, not involve the magnetic origin and magnetic mechanism of materials which is indispensable for revealing the coupling mechanism of metal ions through bridge ligands in magnetic materials.The purpose of this paper is using the first principles based on the density functional theory calculations to study the electronic structure and spin magnetic moments distribution of several coordination compounds, in order to reveal the metal ions through ligand coupling mechanism of the magnetic, which is important for understanding the magnetic origin and magnetic mechanism. In the calculation, we choose based on full-potential linearized augmented plane wave method WIEN2k code, which is one of the most accurate methods for performing electronic structure calculations for crystals.First, the first-principles method was applied to study the electronic structure and magnetic properties of MnCu(pba)(H2O)3·2H2O compound. According to the calculated results, there are two magnetic centers (Cu and Mn ions) in the compound. The Cu-bridge interactions exhibit significant covalent character, while the Mn-bridge interactions are mainly closed-shell interplay. There are strong intrachain interactions and weak interchain couplings. Magnetic coupling exhibits the spin delocalization effect from Mn and Cu atoms to the bridging atoms, and does not reveal metallically magnetic properties. Secondly, the first principle method was applied to study the electronic structure and magnetic properties of the compound of Co(endi)2(N3)2. According to the calculations, there is ferromagnetic interaction between the compound, and the magnetic coupling comes from Co2+ to the azide ligand spin delocalization effect. Also it reveal semi-metallically magnetic properties.Finally, the 2,2’-bipyridine ligands compounds were also studied. It can be seen from the magnetic moment distribution of the compound of Cu(μ-cbdca)(bpy)2, there are the largest magnetic moment distribution on Cu atoms and a small magnetic moment on bipyridine ligand. It indicates that there is ferromagnetic coupling between Cu atoms and the bipyridine ligand, and the ferromagnetic coupling comes from Cu atoms to the bipyridine ligand spin delocalization effect, but does not reveal metallically magnetic properties.更多还原