Al2O3:Fe3+体系晶格局域结构的EPR理论研究

本文通过分析Al2O3∶Fe3+体系中Fe3+离子的EPR谱,研究Fe3+的局域晶体结构结果表明Al2O3∶Fe3+的局域结构存在各向异性膨胀.用拟合EPR谱的低对称参量D和(a-F)实验值的方法,求得两个三棱锥的棱与C3轴的夹角分别为θ1=46.54°和θ2=61.26°,相对于原Al2O3结构的畸变角分别是Δθ1=-1.1°±0.1°,Δθ2=-1.8°.两畸变角同时均小于0说明Al2O3∶Fe3+体系中含Fe3+离子的晶格主要产生沿C3轴的伸长畸变.     

Correlation between Zero-Field Splitting and Site Distortions of Cr^3＋ Ions in NH4Cl：Cr^3＋ System： a Complete Energy Matrix Study

A theoretical method for investigating the inter-relation between the electronic and molecular structures of 3d^3 configuration ions in a tetragonal ligand field is established on the basis of the 120 × 120 complete energy matrices. Using this method, the local structure parameters of two tetragonal Cr^3＋ centers in the NH4 Cl：Cr^3＋ system are determined, Furthermore, the relations between the molecular symmetry and the ligand field symmetry are discussed.     

Cs2 NaMF6(M=Al,Ga):Cr3+络合分子体系局域结构和基态分裂的理论研究

采用双自旋轨道耦合系数模型并结合完全能量矩阵的方法对Cs₂NaMF₆(M=Al, Ga):Cr³⁺ 体系中Cr³⁺ 离子的基态分裂和局域结构进行了研究.通过模拟光谱和EPR谱确定了Cr³⁺ 取代 M³⁺ 形成的两种占位结构的畸变角,发现用双自旋轨道耦合系数模型与单自旋轨道耦合系数模型计算出的畸变角Δθ存在较大的差异.这表     

A density functional theory study on size-dependent structures, stabilities, and electronic properties of the bimetallic MnAgm (M=Na, Li; n+m ≤ 7) clusters

The equilibrium geometries, relative stabilities, and electronic properties of M_nAg_m (M=Na, Li; n+m≤ 7) as well as pure Ag_n, Na_n, Li_n (n≤ 7) clusters are systematically investigated by means of density functional theory. The optimized geometries reveal that for 2≤ n ≤ 7, there are significant similarities in geometry among pure Ag_n, Na_n, and Li_n clusters, and the transitions from planar to three-dimensional configurations occur at n=7, 7, and 6, respectively. In contrast, the first three-dimensional (3D) structures are observed at n+m=5 for both Na_nAg_m and Li_nAg_m cluters. When n+m ≥ 5, a striking feature is that the trigonal bipyramid becomes the main subunit of Li_nAg_m. Furthermore, dramatic odd-even alternative behaviours are obtained in the fragmentation energies, second-order difference energies, highest occupied and lowest unoccupied molecular orbital energy gaps, and chemical hardness for both pure and doped clusters. The analytic results exhibit that clusters with even electronic configuration (2, 4, 6) possess weakest chemical reactivity and more enhanced stability.     

论^6A1基态中Kramers能级的翻转与Hoshina猜想

半导体晶体ＺｎＯ、ＣｄＳ和ＣｄＳｅ具有相似的晶体结构，然而掺入其中的Ｆｅ（Ⅲ）离子却表现出完全不同的基态分裂特征，按顺序ＺｎＯ∶Ｆｅ（Ⅲ）→ＣｄＳ∶Ｆｅ（Ⅲ）→ＣｄＳｅ∶Ｆｅ（Ⅲ）其重要的ＥＰＲ参量Ｄ，将由负值转变成正值，这一变化将导致６Ａ１基态中Ｋｒａｍｅｒｓ能级｜±５／２〉、｜±３／２〉、｜±１／２〉的次序发生翻转。这种奇异的电子能级结构转换现象至１９６７年报道以来迄今未得到合理地解释。Ｈｏｓｈｉｎａ猜想这一现象可能与配位体离子的自旋－轨道耦合系数有关。本文用共价自旋－轨道耦合机制来解释这一能级翻转现象并论证Ｈｏｓｈｉｎａ猜想的正确性     

过渡金属络合分子二步自旋转换量子理论

本文建立了d4,6络合分子二步自旋转换的量子理论.模拟计算得出了如下几点结论:①低对称畸变是d4,6络合分子可以发生二步自旋转换的必要条件;②对于具有任何一种低对称性的任何一种d4,6络合物存在这种低对称畸变的一个临界值,当畸变小于临界值时只可发生一步自旋转换,即HS LS自旋转换;而当畸变大于临界值时则可以发生二步自旋转换,即HS MS和MS LS自旋转换.二步自旋转换导致磁矩曲线上产生两个拐点,与两个自旋转换点相对应,其间的Dq-距离ΔDq随畸变量的增加而增加;③当畸变量等于临界值时络合分子的两个自旋转换点相重迭,即与自旋转换有关的HS、MS、LS三个能级交于一点,这形成一个自旋三相点,它代表一个由三种自旋相形成的临界状态.因此,自旋三相态或许是可以实现的;④低对称畸变将使高自旋磁矩明显增大,可以高于6.10μB.这表明,通常用实验磁矩数据来判断络合物中心为何种离子的方法是不可靠的;⑤低自旋磁矩可以小于1但显大于0,表明在络合分子中过渡金属离子的轨道角动量未完全碎灭的情况.     

Ni2+掺杂到氟化物钙钛矿中的局域结构畸变和基态分裂的理论研究

基于双自旋轨道耦合系数模型并结合完全能量矩阵的方法,研究了AMF₃(A=K, Rb; M=Zn, Cd, Ca):Ni²⁺和K₂ZnF₄:Ni²⁺体系中Ni²⁺的基态分裂和局域结构． 通过模拟光谱和电子顺磁共振(EPR)谱,结果显示在研究氟化物络合分子的能级精细结构和局域结构畸变时,配体F^-对体系的自旋轨道耦合机理的影响不可忽略,同时讨论了EPR参量随夹角、自选轨道耦合、平均参量以及偏离参量的变化规律.     

高压下ErNi2B2C弹性性质、电子结构和热力学性质的第一性原理研究

采用密度泛函理论中的赝势平面波方法研究了高压下超导材料 ErNi₂B₂C 的弹性性质、电子结构和热力学性质.分析表明, 弹性常数、体弹模量、剪切模量、杨氏模量和弹性各向异性因子的外压力效应明显. 电子态密度(DOS)的计算结果显示, 在费米能级(E_F)处的 DOS 峰随外界压强的增大显著降低, 由于 ErNi₂B₂C 相对较高的超导温度(T_c)起因于E_F处的 DOS 峰, 因此推测压强增大可能会降低 ErNi₂B₂C 的 T_c.类似的现象在超导材料 MgB₂和 SrAlSi 中已被发现.此外, 基于准谐德拜模型, 对 ErNi₂B₂C 在高温高压下的热力学性质的研究表明, 在一定范围内, 温度和压强将对其热膨胀系数和热容产生明显的影响. 关键词： 高压 弹性性质 电子结构 热力学性质     

Zero-field splitting parameters and local structures for tetragonal Cr2＋ centers in Cr2＋-doped ZnSe semiconductors

The inter-relation between zero-field splitting （ZFS） parameters and local lattice structures of the （CrSe4）6 clusters in ZnSe semiconductors has been established by using the complete diagonalization （of the energy matrix） method. On the basis of this, the local lattice distortions, the ZFS parameters D, a, F and the optical spectrum for Cr2＋ ions doped into ZnSe are theoretically investigated, and the contributions of the spin singlets have been taken into account. The calculated ZFS parameters are in good agreement with the experimental values. From our calculations, the tetragonal distortion parameters AR = 0.091A and Aθ = 4.28° of Cr2＋ in ZnSe are acquired, and the results suggest that there exists a tetragonal expansion distortion for the local lattice structure of （CrSe4）6- clusters in ZnSe crystals. The influence of the spin singlets on ZFS parameters is also discussed, indicating that the contributions to ZFS parameters a and F cannot be ignored.     

Theoretical investigations of the local distortion and electron paramagnetic resonance parameter for CdCl2：V^2＋ and CsMgX3：V^2＋（X=Cl,Br） systems

This paper systematically investigates the local distortion and electron paramagnetic resonance (EPR) parameter for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems on the basis of the complete energy matrix, in which not only the contributions due to the spin–orbit coupling of the central ions but also that of the ligands are considered. To describe the difference of overlapping between d-orbits and p orbit, two spin–orbit coupling coefficients are introduced. By simulating the crystal field parameter and EPR parameter, the local distortion parameters are studied and the relationships between the EPR parameter and the spin–orbit coupling coefficients as well as divergent parameter are discussed. These results show that the local structures exhibit compression distortion for CdCl 2 :V 2+ and elongation distortions for CsMgX 3 :V 2+ (X=Cl, Br), respectively. It notes that the empirical formula R ≈ R H + (r i-r h )/2 is not suitable for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br) systems. The contributions of ligand to spin–orbit coupling interaction cannot be neglected for strong covalent systems, especially for V 2+ doped in CsMgBr 3 :V 2+ .