C72,La2@C72几何结构和电子性质的计算研究

采用密度泛涵理论(density functional theory, DFT)中的广义梯度近似(generally gradient approximation, GGA)对富勒烯C₇₂和内掺金属La富勒烯La₂@C₇₂三种同分异构体的几何结构和电子结构进行研究.发现在C₇₂的三种同分异构体中，满足独立五边形规则(isolated-pentagon-rule，IPR)的C₇₂(D_{6d< 关键词： 72}')" href="#">C₇₂ 2@C₇₂')" href="#">La₂@C₇₂ 密度泛涵理论 几何结构 电子结构     

Ce4+离子在Ca2SnO4一维结构基质中的电荷迁移光谱研究

利用高温固相反应法制备了Ca₂Sn_1-xCe_xO₄和Ca_2-ySr_ySn_1-xCe_xO₄一维结构发光体. XPS结果显示 Ca₂SnO₄拥有两种结合能分别为5277 eV和5293 关键词： 2Sn_1-xCe_xO₄')" href="#">Ca₂Sn_1-xCe_xO₄ 2-ySr_ySn_1-xCe_xO₄')" href="#">Ca_2-ySr_ySn_1-xCe_xO₄ 一维结构 电荷迁移光谱     

AlO2和Al2O分子的结构与解析势能函数

运用密度泛函理论的B3LYP方法在6-311++G^**水平上,对AlO₂,Al₂O分子的结构进行了优化计算,得到AlO₂,Al₂O分子的稳定结构都为D_∞h构型.　AlO₂电子态为X²Π_u,平衡核间距R_Al-O关键词： 2')" href="#">AlO₂ 2O')" href="#">Al₂O Murrell-Sorbie函数 多体项展式理论     

Pu3体系的结构与势能函数

用相对论有效原子实势(RECP)和密度泛函(B3LYP)方法对Pu_n(n=2,3)体系的结构进行了优化,得到了Pu₂和Pu₃分子的几何构型分别为D_∞h,D_3h,其基态分别为13和19重态.在B3LYP/RECP水平上得到Pu₂分子的光谱常数ω_e=52.3845cm^-1,ω_e　χ_e=0.02 关键词： 2')" href="#">Pu₂ 3')" href="#">Pu₃ 分析势能函数     

内掺过渡金属富勒烯衍生物Ni@C20H20几何结构、成键和电磁性质的密度泛函计算研究

采用密度泛函理论中的广义梯度近似对Ni@C₂₀H₂₀的几何结构、成键和电磁性质进行密度泛函计算研究.结构优化发现位于偏离笼子中心三种位置处的Ni原子优化之后均回到笼子中心.结合能和能隙分析表明C₂₀H₂₀的中心位置是Ni原子热力学和动力学最稳定的位置.成键分析表明：Ni原子位于C₂₀H₂₀中心时,和C原子之间几乎没有相互作用,保持自己的孤立状态.电磁分析表明：原子磁矩为2关键词： 20H₂₀')" href="#">C₂₀H₂₀ 20H₂₀')" href="#">Ni@C₂₀H₂₀ 几何结构 成键 电磁性质 密度泛函理论     

BeH,H2和BeH2的分子结构和势能函数

用二次组态相关(QCISD)和密度泛函(B3LYP)方法, 选用6-311++g(d,p), 6-311++g(3df,3pd)和D95(3df,3pd)基组对H₂, BeH和BeH₂分子的结构进行优化. 得到它们的基态电子态分别为H₂(¹Σ_g), BeH(²Σ)和BeH₂(¹Σ_{g 关键词： BeH 2}')" href="#">BeH₂ 2')" href="#">H₂ 二次组态相关(QCISD) 势能函数     

BH2的分子结构和势能函数

采用密度泛函理论(DFT)的B3P86方法和相对论有效原子实势理论模型(RECP)，对BH₂，BH₂⁺和BH₂^-分子进行了优化，得到这些分子基态的电子状态分别是²A′，³A′，³A″. 计算也得到了BH₂的分子结构和势能函数，它的离解能是7.752eV，BH₂分子具有C_{2V关键词： 2}')" href="#">BH₂ 分子结构 势能函数     

V+注入锐钛矿TiO2第一性原理研究

用金属离子注入方法在锐钛矿TiO₂薄膜中掺杂了V⁺，采用全势线性缀加平面波方法计算了锐钛矿TiO₂及V⁺掺杂TiO₂超原胞的电子结构，通过紫外-可见吸收光谱测试方法检测了注入不同剂量的V⁺对TiO₂薄膜吸收光谱的影响.理论计算和实验结果表明，锐钛矿TiO₂薄注入V⁺后，带隙宽度变小，吸收光谱发生红移，并且TiO 关键词： +注入')" href="#">V⁺注入 2')" href="#">TiO₂ 全势线性缀加平面波方法 能带结构     

金属间化合物PrMn6Sn6的结构、磁性与119Sn穆斯堡尔谱研究

采用电弧熔炼法制备了金属间化合物PrMn₆Sn₆.X射线衍射表明该化合物具有HoFe₆Sn₆型(空间群为Immm)晶体结构.磁测量表明该化合物为铁磁性，居里温度为325　K.在15—360　K范围内测量了¹¹⁹Sn穆斯堡尔谱，得到了8个Sn原子晶位的转移超精细场随温度的变化，并且讨论了Mn亚晶格与Pr亚晶格的磁有序方向. 关键词： 6Sn₆')" href="#">PrMn₆Sn₆ 穆斯堡尔谱 磁结构     

密度泛函理论研究Scn，Yn和Lan(n=2—10)团簇的稳定性、电子性质和磁性

通过采用密度泛函理论对Sc₂,Y₂和La₂基本性质的计算,选择在较优理论水平下系统地研究了Sc_n, Y_n和La_n(n=2—10)团簇的几何结构、稳定性、电子性质和磁性及其随团簇尺寸的变化趋势.此同族三种团簇的稳定性由原子密堆集几何结构效应决定,幻数均表现出一致的结果.La_n团簇的能隙比 关键词： n')" href="#">Sc_n n和La_n团簇')" href="#">Y_n和La_n团簇 密度泛函理论 电子性质 磁矩     

强耦合磁失措自旋冰系统Dy2Ti2O7单晶生长和基本磁性质测量

利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy₂Ti₂O₇单晶体.X射线衍射实验证实晶体具有面心立方结构，空间群为Fd3m，晶胞参数a＝1.0112(2) nm，［111］和［400］方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10^-5 m³/mol，有效磁矩μ_eff＝10.24(4)μ_B，Cure-Weiss温度Θ_CW＝1.1 K，揭示Dy₂Ti₂O₇具有弱的铁磁性.对磁性起源的综合分析表明，该自旋冰晶体磁性质主要来源于磁偶极相互作用，且相关最近邻长程偶极相互作用能量标度D_nn＝3.00 K. 关键词： 2Ti₂O₇')" href="#">Dy₂Ti₂O₇ 浮区法晶体生长 关联电子系统 自旋冰     

Theoretical studies of the defect structures and spin Hamiltonian parameters for manganese(II) and nickel(II) doped Zn(en)3(NO3)2 single crystals

The spin Hamiltonian parameters (g factors, hyperfine structure constants and zero-field splittings D and E) and local structures for Mn²⁺ and Ni²⁺ in [Zn(en)₃](NO₃)₂ single crystal are theoretically investigated from the perturbation calculations for trigonally distorted 3d⁵ and trigonally (or orthorhombically) distorted 3d⁸ cluster. The trigonal Mn²⁺ and Ni²⁺ centres are found to undergo the moderate angular variations Δβ of 4.5° and 5.2°, respectively, related to host Zn²⁺ site due to size mismatch. The orthorhombic Ni²⁺ centre shows the relative axial elongation ratio ρ (≈ 2.5%) and the relative perpendicular bond length variation ratio τ (≈0.2%). For Mn²⁺ centre, the contributions to g-shifts Δg_CT (or hyperfine structure constants A_CT and zero-field splitting D_CT) from charge-transfer (CT) mechanism are opposite in sign and five times (or 5% and 8%) in magnitude compared with those from crystal-field (CF) mechanism. For the trigonal Ni²⁺ centre, Δg_CT (or D_CT) are the same (or opposite) in sign and 17% (or 2%) in magnitude related to those from CF mechanism. For the orthorhombic Ni²⁺ centre, Δg_CT and E_CT (or D_CT) are same (or opposite) in sign and 16% and 48% (or 442%) in magnitude with respect to those from the CF mechanism. The signs and magnitudes of the trigonal distortion angles δβ (≈ ?0.3 and 0.4°) related to an ideal octahedron and the local angular variations Δβ related to the host bond angle are suitably illustrated by those of the axial distortion degree (ADD) and the angular variation degree (AVD) of the systems, respectively.     

119Sn Mössbauer study of nickel–tin anodes for rechargeable lithium-ion batteries

¹¹⁹Sn Mössbauer spectrometry has been carried out on Ni–Sn alloys (Ni₃Sn LT, Ni₃Sn₂ LT and Ni₃Sn₄) and combined with ab initio calculations. Lithium insertion/extraction mechanisms of the most interesting compound (Ni₃Sn₄) have been studied from ¹¹⁹Sn Mössbauer measurements. The first discharge shows a plateau close to 0.0 V, which can be attributed to the formation of the Li₇Sn₂ alloy.     

Tb2AlFe16-xMnx化合物的结构、磁性及正电子湮没谱研究

通过X射线衍射、磁测量及正电子湮没谱等手段研究了Tb₂AlFe_16-xMn_x（x=1—8）化合物的结构和磁性.X射线衍射研究结果表明Tb₂AlFe_16-xMn_x化合物具有六角相的Th₂Ni₁₇型结构.室温下的正电子湮没实验研究表明,Mn对Fe的替代导致化合物中的铁磁相互作用减弱,并且化合物中存在着较强烈的磁弹耦合效应.磁测量研究结果表明,Mn的替代导致Tb₂AlFe_16-xMn_x化合物的居里温度及自发磁化强度急剧下降. 关键词： 2AlFe_16-xMn_x化合物')" href="#">Tb₂AlFe_16-xMn_x化合物 磁弹耦合效应 居里温度     

Martensitic phase transition with magnetocaloric effect and double-shifted exchange bias in the martensitic phase for Ni48Mn39Sn13-xGex alloys

Ni₄₈Mn₃₉Sn_13-xGe_x (x?=?1, 2) Heusler alloys have been prepared, and the martensitic phase transition (MPT), magnetocaloric effect and exchange bias (EB) have been explored. At room temperature, the structure of both samples presents L2₁ type, and the MPT shifts to a higher temperature, while the Curie temperature (T_C) of the austenitic phase decreases with the increase of the Ge content. The maximum magnetic entropy change of Ni₄₈Mn₃₉Sn_13-xGe_x with x?=?2 reaches about 14.67?J/kg?K under the magnetic field of 5?T during reverse MPT. In addition, an interesting phenomenon is the enhancement of EB with the increase of the Ge content, especially the abnormal presence of the double-shifted hysteresis loop has been realized in Ni₄₈Mn₃₉Sn_13-xGe_x with x?=?2, which can be interpreted by the fact that the antiferromagnetic (AFM) regions couple with proximal ferromagnetic (FM) regions in the opposite way at low temperature.     

Exploring CP violation and penguin effects through B0d→D+D- and B0s→D+sD-s

The decay B⁰ _d→D⁺D^- offers an interesting probe of CP violation, but it requires control of penguin effects, which can be done through B⁰ _s→D⁺ _sD^- _s by means of the U-spin flavour symmetry of strong interactions. Recently, the Belle collaboration reported indications of large CP violation in the B⁰ _d decay, which were, however, not confirmed by BaBar, and first signals of the B⁰ _s channel were observed at the Tevatron. In view of these developments and the quickly approaching start of the LHC, we explore the allowed region in observable space for CP violation in B⁰ _d→D⁺D^-, perform theoretical estimates of the relevant hadronic penguin parameters and observables, and we address questions both about the most promising strategies for the extraction of CP-violating phases and about the interplay with other measurements of CP violation and the search for new physics. As far as the latter aspect is concerned, we point out that the B⁰ _q→D_q ⁺D^- _q system provides a setting for the determination of the B⁰ _q–B̄⁰ _q mixing phases (q∈{d,s}) that is complementary to the conventional B⁰ _d→J/ψK_S and B⁰ _s→J/ψφ modes with respect to possible new-physics effects in the electroweak penguin sector.     

立方体AgCl微晶中［Fe(CN)6］4-引入的浅电子陷阱阱深与俘获截面的动力学模拟

为了描述在晶体生长阶段掺入［Fe(CN)₆］^4-的立方体AgCl微晶中 光电子的产生与 衰减过程，建立了一种由三个固有中心和一个浅电子陷阱(SETs)组成的动力学模型，并引出一组微分方程.通过求解微分方程得到与实验结果相符合的光电子衰减曲线及其寿命.调整相 关模拟参数，于常温下得到由［Fe(CN)₆］^4-引入的SETs阱深为0.1 15eV，电子俘获截面为2.136×10^-17cm². 关键词： 光电子 浅电子陷阱 俘获截面 AgCl微晶     

Investigation of total and partial magnetic moments of Mn2NiAl with pressure at a several temperatures

ABSTRACT

The first principles calculations of structural and magnetic properties of the Heusler material Mn₂NiAl, have been studied using a full potential linearized augmented plane wave (FP-LAPW) within the density-functional theory (DFT). The phase stability of the cubic austenitic (L2₁₎ structure for Mn₂NiAl in both Cu₂MnAl (Fm3?m space group) and Hg₂CuTi (F43?m space group) type of structures with ferromagnetic and antiferromagnetic states, has been treated by applying the generalized gradient approximation proposed by Wu and Cohen (WC-GGA) alongside with the martensitic structure of Mn₂NiAl. The analysis of phase stability, cohesive energy and the calculated formation enthalpy of Mn₂NiAl reveal that the ferromagnetic MnMnNiAl is the most stable type of structure. Moreover, the calculated lattice parameters are found to be in good agreement with theoretical data. The variation of total magnetic moments M_T(μ_B), M_Mn (μ_B), M_Ni (μ_B) and M_Al (μ_B) in Mn₂NiAl with pressure at varying temperature (0, 273 and 344?K), have been calculated.     

Comparative analysis of crystal field effects and energy level scheme of six-fold coordinated Cr ion in the pyrochlores, Y2B2O7 (B=Ti, Sn)

The electronic energy levels of the six-fold coordinated Cr⁴⁺ ion in the pyrochlores Y₂B₂O₇ (B=Sn⁴⁺, Ti⁴⁺), have been computed using the exchange charge model of crystal field theory. The calculated Cr⁴⁺ energy levels and their trigonal splitting are in good agreement with experimental spectra. Calculations of the crystal field parameters show that the higher crystal field strength in Y₂Sn₂O₇ (in comparison with Y₂Ti₂O₇) arises from increased orbital overlap effects between the Cr⁴⁺ ion and the nearest oxygen ions, which are located at the 48f crystallographic position of the pyrochlore lattice. The increased overlap in Y₂Sn₂O₇ occurs despite the fact that the Cr⁴⁺-O^2- bond distance in Y₂Sn₂O₇ is longer than in Y₂Ti₂O₇. This is attributed to a lack of hybridization (covalent bonding) between the filled 2p orbital of oxygen ion occupying the 48f site of the pyrochlore lattice and the filled Sn⁴⁺ 4d¹⁰ orbital. As a result, a stronger crystal field is experienced by Cr⁴⁺ ions in Y₂Sn₂O₇, even if the Cr⁴⁺-O²⁻ distances are greater in this case, when compared to those in Y₂Ti₂O₇.     

立方对称晶场中6S(3d5)态离子的磁相互作用及其自旋哈密顿参量的微观起源

基于完全对角化方法(complete diagonalization method, CDM), 研究了⁶S(3d⁵)态离子在立方对称晶场中的磁相互作用,分析了自旋哈密顿参量(a, g,Δg)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同时考虑了SS(spin-spin),SOO(spin-other-orbit),OO(orbit-orbit)磁相互作用.研究表明：⁶S(3d⁵)态离子在立方对称晶场中的自旋哈密顿参量起源于五种机理,即SO机理,SS机理,SOO机理,OO机理以及SO-SS-SOO-OO联合作用机理.文中研究了五种机理的相对重要性,结果表明：SO机理与SO-SS-SOO-OO联合作用机理在五种机理中最为重要.尽管SS,SOO,OO磁相互作用单独作用时对自旋哈密顿参量的贡献很小,但它们的联合作用SO-SS-SOO-OO机理对自旋哈密顿参量的贡献非常可观.此外研究表明：零场分裂参量a主要来自纯自旋四重态及自旋二重态与自旋四重态联合作用的贡献,而Zeemang(或者Δg)因子主要来自纯自旋四重态的贡献.纯自旋二重态对自旋哈密顿参量a与g(或者Δg)的贡献为零.在我们所选择的晶场区域,发现下列关系始终成立：a>0,a(-|Dq|)<a(|Dq|),g(-Dq)=g(Dq),a(-Dq,-ξ_d,B,C)=a(Dq,ξ_d, B,C),Δg(-Dq,-ξ_d, B, C)=Δg(Dq,ξ_d, B, C).作为本文理论的应用,研究了四种典型的Mn²⁺掺杂晶体材料,即Mn²⁺:KZnF₃,Mn²⁺: RbCdF₃,Mn²⁺: MgO,Mn²⁺: CaO,理论与实验测量符合很好. 关键词： 自旋哈密顿参量 6S(3d⁵)态离子')" href="#">⁶S(3d⁵)态离子 磁相互作用 完全对角化方法(CDM)