Fe_nO_m~+(n+m=4)团簇的构型、电子结构特征和磁性

采用二项式方案构建了FenOm+(n+m=4)团簇的大量可能初始结构.运用广义梯度近似(GGA)密度泛函理论中的PW91交换关联泛函对这些初始结构进行优化和频率分析,得到12个稳定的异构体.在此基础上计算和分析了它们的结合能、对称性、键长、磁矩,最高占据轨道与最低未占据轨道的能隙.发现Fe—O键在FenOm+(n+m=4)团簇的稳定中具有重要作用,团簇的总磁矩主要取决于铁原子的磁矩和各个原子磁矩排布情况.     

Synthesis,Structure, and Magnetic Properties of Di-μ-Pyrazolatodicopper(II) Complexes of 3,5-Bis(Aminomethyl)Pyrazole

Abstract

3,5-Bis(aminomethyl)pyrazole (Hbampz) forms binuclear copper(II) complexes of the formula [Cu₂(bampz)₂X₂] (X = CI, Br). The crystal structure of [Cu₂(bampz)₂Br₂] has been determined by the X-ray method: formula = CuBrN₄C₅H₉, monoclinic, space group P2₁/n, a = 9.214(1), b = 10.078(1), c = 8.775(1) Å, β = 97.33(1)°, V = 808.1 ų. Two bampz^? molecules combine with two copper(II) ions via the pyrazolate nitrogen and aminonitrogen atoms in the side chains affording an essentially planar N₄ environment for each metal ion. The Cu-Cu separation is 3.947(5)A. The axial site of each copper is weakly coordinated by a bromide ion with a Cu-Br distance of 2.895(4) A. Cryomagnetic investigations over the temperature range 80-300 K revealed a significant antiferromagnetic interaction through the pyrazolate bridges. The exchange integrals (J) based on the Heisenberg model (H =—2J?₁.?₂) was estimated at—200.8 and—192.0 cm^?1 for [Cu₂(bampz)₂Cl₂] and [Cu₂(bampz)₂Br₂], respectively.     

应变作用下量子顺电材料EuTiO3的磁电性质

由于磁性和介电性质的强烈耦合, 量子顺电材料EuTiO₃材料的研究近来倍受人们的关注. 本文通过运用基于密度泛函理论的第一性原理计算研究了量子顺电(PE) 材料EuTiO₃的磁性和电子结构, 分析了应变对磁性和结构相变的作用, 从而探讨了该材料中可能的磁电耦合机理. 结果发现, 在无应变状态下, EuTiO₃处于顺电立方-G型反铁磁性态, 而对于c轴方向的无论张应变还是压应变, 当应变增加到一定程度时, 由于Ti 3d空轨道与周围O 2p 电子的杂化平衡被打破, EuTiO₃将相变到铁电( FE) 四方-铁磁结构, 显示了强烈的自旋-晶格耦合效应.     

Magnetism and superconductivity in ErNi2B2C

We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal ErNi₂B₂C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature, T _F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal to square transition as a function of applied field. Further distortions of the vortex lattice occur at T _N, but no changes are seen at T _F.     

Irrelevant operators and momentum-shell recursion relations ind=2 + ∈ dimensions

The momentum-shell recursion relations of Nelson and Pelcovits for ann-vector model near two dimensions are reexamined. The renormalization of the infinite set of relevant and marginal operators present in the system is studied. Ambiguities obtained in the ensuing recursion relations are shown to involve irrelevant operators only, thus justifying the procedure of Nelson and Pelcovits. The cases of finite external fieldh and finite spin anisotropyg are both considered.     

Surface magnetism of real iron borate monocrystals

A theory of the surface magnetism of iron borate, FeBO₃, allowing for the non-ideality of the crystal structure of the near-surface layer is constructed. Since the magnetizing field of a near-surface layer appears to be inversely proportional to the tenth power of the crystal lattice parameter, the influence of the non-ideality on the surface magnetism should be substantial. The suggested models of reconstruction make it possible to describe experiments if the magnitude of the deformations is in agreement with literature data. The theoretical dependence of the value of the surface anisotropy on the concentration of point defects in a near-surface layer of the crystal is also established.     

N，N′-双(3-羧基水杨醛叉缩胺乙基)草酰胺均双核铜(II)的密度泛函研究

草酰胺及其衍生物过渡金属原子配合物是近年来在实验和理论上[1￣5]研究都十分活跃的领域,其原因是这些配合物具有良好的磁性质,对磁功能分子设计和磁性材料合成有着十分重要的意义。我们课题组合成了一种以N,N′-双(3-羧基水杨醛叉缩胺乙基)草酰胺为配体的Cu!-Cu!均双核配合物,由于该配合物的溶解性较差,难以培养出理想的单晶,因此一直未曾进行晶体结构解析。所以,该配合物分子的电子结构特征和几何构型,电子结构与配合物分子的稳定性及分子的磁性之间的构效关系等目前尚不清楚。因此,就该类磁功能配合物分子的上述问题进行理论研究,无疑…     

单核Cu(Ⅱ)配合物C_(18)H_(12)CuN_4O-2的密度泛函研究

用量子化学从头算方法,在ROB3LYP/LANL2MB水平上,对单核配合物C18H12CuN4O2进行了理论计算,优化得到了该配合物的平衡几何构型,并计算了它的谐振动频率.结果表明:该配合物分子是可以稳定存在的,电子自旋布居主要集中在Cu原子及配体原子上,Cu原子和配体原子的自旋布居符号相同,说明体系中存在较强的自旋离域效应.体系的前沿轨道主要由Cu原子的d轨道和配体原子的p轨道组成,这种组成有利于配体与磁中心之间的电子转移.计算结果与实验符合得较好.     

有机光致变色自由基化合物研究进展

综述了近年来有机光致变色自由基化合物的研究进展, 着重介绍了联茚满烯二酮类自由基衍生物的发展. 对自由基的生成和变色机理做了较为细致的介绍.