BaVS3晶格动力学研究

采用基于密度泛函理论的平面波赝势方法,在局域密度近似下采用线性响应的密度泛函微扰理论研究了具有六角结构的BaVS₃化合物的晶格动力学性质,得到了整个声子谱.计算得到的Γ点拉曼频率和实验数据进行了比较,其中E²_2g模、A_1g模和实验测量值符合得比较好.对于E³_2g模,采用线性响应计算的结果与实验值差别较大.对该模应用冻结声子方法研究后认为差异主要是由于E³_2g模的较强的非谐性引起的.此外V原子在平面内的振动模E¹_2u出现了虚频.虚频的出现预示着六角相的BaVS₃结构的不稳定性,从而很好地解释了该材料由六角相到正交相的结构相变. 关键词： 晶格动力学 密度泛函 赝势方法 3')" href="#">BaVS₃     

具有D4h对称性构型的C42+分子的Jahn-Teller效应与能级分裂

依据量子理论与配位场理论,利用群论和对称性分析的方法探讨了C42+分子在具有D4h对称性构型时,E(b1g+b2g)系统的Jahn-Teller效应中的相关问题.研究了C42+分子的电子态与声子态的对称性及其活跃声子态,讨论了系统声子间的耦合与CG系数,构建了E(b1g+b2g)系统的电声耦合哈密顿量,利用幺正平移变换将系统变换到了无声子激发的空间中,由此计算出了系统无声子激发的基态与激发态及其能级,结果表明由于系统的电声耦合作用缘故,在系统的势能面上形成了四个对称性势阱.无论系统处在哪一个势阱中,在Jahn-Teller畸变之后,系统的二重简并的能级都将发生分裂,分裂后系统电子态的简并性完全被消除.文中利用群论又进一步探讨了系统的Jahn-Teller畸变方向及其基态对称性,发现系统将沿着D4h→D2h方向发生畸变.畸变后C24+分子的基态具有D2h群下的B1u对称性.     

LaCoO3中自旋态转变现象的超声研究

测量了LaCoO₃单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自 旋态转变温度附近（≈90K），纵波声速出现明显的软化并伴随一个尖锐的衰减峰，但是在 横波的测量中却没有出现类似的超声异常，分析认为LaCoO₃在90K附近的自旋态 转变是由于Co³⁺离子是从低自旋态(LS,t⁶_2ge⁰ _g)转变到中等自旋态(IS,t⁵ _2ge¹_g )，而不是高等自旋态(HS,t⁴_2ge²_g).随着温度的升高，在 200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰，这可能是随 机分布的IS态Co³⁺离子的Jahn-Teller效应导致的局域晶格扭曲所造成的. 关键词： 超声声速与衰减 自旋态转变 Jahn-Teller效应     

第一性原理计算MgB2薄膜拉伸对超导电性的影响

应用全势线性响应线性糕模轨道方法计算MgB₂的电子能带结构、声子谱及电声子耦合常数,并讨论MgB₂的超导电性.通过比较MgB₂薄膜双轴拉伸前后超导电性的变化可以看出，随着a轴晶格常数增大和c轴晶格常数减小,声子谱中硼的E_2g声子频率显著下降，使得电声子耦合强度λ和声子对数平均频率ω_ln增强,提高了MgB₂薄 关键词： 超导电性 能带结构 声子频率 电声子耦合     

乙醚团簇的激光电离质谱及从头计算

应用激光多光子电离质谱与超声脉冲分子束技术研究了乙醚团簇，实验中观测到乙醚的碎片离子以及强度较小的(E)H⁺，(E)^＋₂和(E)₂H⁺(E代表CH₃CH₂OCH₂CH₃)，没有发现更大尺寸的团簇离子.结合从头计算理论，在B3LYP/6-311++G(d,p 关键词： 乙醚团簇 偶极-偶极相互作用 从头计算     

Cu1-xHxZr2(PO4)3中Cu2+的EPR谱和局域结构研究

本文采用Cu²⁺斜方对称电子顺磁共振（EPR）参量的高阶微扰公式计算了晶体Cu_1-xH_xZr₂（PO₄）₃中Cu²⁺的EPR参量（g因子和超精细结构常数A因子）．计算结果表明，晶体Cu_1-xH_xZr₂（PO₄）₃中[CuO₆]^10-基团的Cu-O键长分别为R_||≈0.241 nm，R_⊥≈0.215 nm，平面键角τ≈80.1°；由于对称性降低，中心金属离子基态²A_1g（θ）和²A_1g（ε）有一定程度混合，混合系数α≈0.995．所得EPR谱图的理论计算值与实验数据符合得很好．     

124Te核1+态和高自旋态能谱特征的微观研究

利用微观sdIBM-2+2q.p.方案，成功地计算出¹²⁴Te核的低自旋态和部分高自旋态，特别是较成功地再现了1⁺₁,1⁺₂,3⁺₁，3⁺₂和5⁺₁态.基于该方案推出的能量关系指认：6⁺₁，8⁺_{关键词： 能谱特征 拆对与顺排 微观sdIBM-2+2q.p.方案 124Te核')" href="#">¹²⁴Te核}     

H+5团簇离子及其中性团簇产物H3和H4

报道了H⁺₅的实验结果.分析讨论了H⁺₅的 形成和分解途径.根据理论分析，以稳定的H⁺₃为核心与一个或多个氢分子结合可能形成稳定的H^{+_n氢团簇离子.另一方面，在高频离子源中, 有发生H+₃与H₂反应的条件.实 验中，从高频离子源引出的离子束被静电加速器加速，然后用9 关键词： +}₅团簇离子')" href="#">H⁺₅团簇离子 3中性团簇')" href="#">H₃中性团簇 4中性团簇')" href="#">H_{4中性团簇}     

281—332nm SO+2的光碎片激发谱研究

在超声分子束条件下，利用380.85nm的电离激光使SO₂分子经由［３＋１］共 振增强多光 子电离(REMPI)制备纯净的分子离子SO⁺₂(²A ₁(000))，用另一束解离激光在281 —332nm扫描获得了光解碎片激发(PHOFEX)谱.获得的光碎片SO⁺激发谱基本可以 归属为SO ⁺₂(,)←SO⁺关键词： +₂')" href="#">SO⁺₂ 光解离 光碎片激发谱     

甲烷分子电子碰撞电离和解离的实验研究

本文利用反应显微成像技术(reaction microscope)研究了54 eV电子入射甲烷分子导致的电离解离过程,详细分析了电离解离产生的CH⁺₂,CH⁺,C⁺离子碎片的动能分布情况.实验结果表明,该入射能量下产生CH⁺₂,CH⁺,C⁺离子碎片主要贡献来自2a₁内价轨道电子的直接电离过程产生的离子态(2a< 关键词： 反应显微成像谱仪 电离解离 能量沉积 动能分布     

Theoretical study of the electronic structure of a tetragonal chromium(III) complex

The low-temperature single-crystal polarized absorption and the luminescence spectra of Cs₂[CrCl₂(H₂O)₄]Cl₃ are theoretically analyzed in order to determine the electronic structure of the trans-[CrCl₂(H₂O)₄]⁺ complex. This study, based on the Racah theory, leads to a good agreement between the theoretical and experimental energy levels. The electronic-exited state ⁴T_2g(O_h) is split into ⁴E_g and ⁴B_2g components due to the lowering of the symmetry from O_h to D_4h. The polarized absorption spectrum and the theoretical energies show that the ⁴E_g(D_4h) state is lower in energy than the ⁴B_2g(D_4h) state. The resolved vibronic structure in the luminescence spectrum reveals a progression in a non-totally symmetric b_1g mode, a manifestation of a Jahn-Teller effect in the emitting state ⁴T_2g(O_h). Both Jahn-Teller and spin-orbit coupling in the orbitally degenerated ⁴E_g(D_4h) state are necessary to account for the spectroscopic observations.     

C42+的几何构型和Jahn Teller效应

用从头计算法QCISD/6-311G得到了C₄²⁺分子的10种不同的几何构型,其中包括C_s,C_∞v,C_2v,D_2h,D_∞h,D_4h,D_2d,C_3v等不同的构型.计算表明C₄²⁺的T_d构型不能稳定存在,详细讨论了T_{d 关键词： 几何构型 4}²⁺')" href="#">C₄²⁺ Jahn Teller效应     

Theoretical studies on the SH parameters and local distortion structure of KCl:Ag crystal

Complete diagonalization of the energy matrix and high order perturbation formulae of spin-Hamiltonian (SH) parameters possessing D_4h symmetry for the 4d⁹ ion based on the crystal- and ligand-field theory in tetragonal symmetry are expressed and applied to the study of local distortion structure of the KCl:Ag²⁺ crystal. The calculated results agree well with experimental findings. Both complete diagonalization of energy matrix and high order perturbation approach are appropriate for the investigations of SH parameters of 4d⁹ ions in tetragonal crystals. Tetragonal distortion due to the Jahn-Teller effect for the tetragonal Ag²⁺ center at the K⁺ site of KCl crystal is also acquired from the calculations.     

Topological representations of Jahn-Teller distortions

Topological representations (top-reps), which originally were developed to model molecular polyhedral isomerization processes, can be extended to depict the relationships between the polygons and polyhedra involved in Jahn-Teller (JT) distortions. Using this approach, the top-rep of the E ? (b _1g + b _2g) distortion of square planar molecules to rectangle and rhombus isomers becomes a rhombus in which the vertices alternately represent distortions to the rectangle and rhombus isomers. Similarly the top-rep of the E ? e distortion of regular O_h octahedra to elongated D_4h tetragonal bipyramids becomes a triangle in which the vertices represent the three distinct tetragonal bipyramids from a given octahedron and the edge midpoints represent lower symmetry rhombic D_2h intermediates. A regular octahedron can be used as a top-rep for the T ? (e + t ₂) distortions of regular octahedra if the 6 vertices represent distortions to D_4h tetragonal bipyramid isomers, the 8 face midpoints represent distortions to D_3d trigonal antiprism isomers, and the 12 edge midpoints represent lower symmetry rhombic D_2h intermediates. In the case of Jahn-Teller T ? h distortions of regular I_h icosahedra, the corresponding top-rep becomes a regular icosahedron in which the 12 vertices represent distortions to pentagonal D_5d isomers, the 20 face midpoints represent distortions to trigonal D_3d isomers, and the 30 edge midpoints represent D_2h intermediates. A 4-dimensional analogue of the tetrahedron (i.e. the 4-simplex) can be used as a top-rep for the G ? g problem and the H ? g component of the H ? (g + 2h) problem for JT distortions of regular icosahedra. In this case the 5 vertices and the 10 edge midpoints correspond to T_h isomers and D_3d intermediates, respectively.     

BeH2(X1Σ+g)与H2S(X1A1)分子的结构与解析势能函数

运用单双取代二次组态相关(QCISD)方法,在6-311++G(3df,3pd)基组水平上,对BeH₂和H₂S分子的结构进行了优化计算,得到基态BeH₂分子的稳定结构为D_∞h构型,电子态为X¹Σ⁺_g,平衡核间距R_BeH=0.13268nm,R_{关键词： 2}')" href="#">BeH₂ 2S')" href="#">H₂S Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Pseudo-Jahn–Teller effect in Si4X4 (X = F,Cl, Br,I) molecules: a theoretical investigation

ABSTRACT

The variability of planar rings in Si₄X₄ (X?=?F, Cl, Br, I) molecules caused by the pseudo-Jahn–Teller impact (PJTE) was evaluated as an original PJTE work. Optimisation and the following frequency calculations in these molecules illustrated that in high-symmetry planar (with D_4h symmetry) geometry, all of these compounds were unstable and their structures were puckered to lower C_2h symmetry stable geometry. Furthermore, the vibronic coupling interaction between ¹A_1g ground and the first ¹E_g excited states through (¹A_1g?+?¹E_g) ? e_g PJTE problem was the cause of non-planarity of the four-member ring and the symmetry breaking phenomenon in those series. The calculated gaps (Δ) between the ground state and the E_g excited state, the vibronic coupling (F) and ground state primary force constant values (k₁) were obtained from the numerical fitting of the ground state adiabatic potential energy surface with the analytical expressions of these molecules. Finally, natural bond analysis (NBO) was used for the design of the strongest interaction and natural atomic charges of these structures.     

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     

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     

Mechanical and electronic properties of endofullerene Ne@C60 studied via structure distortions

Elastic, strength, electronic properties and vibrational spectra of Ne@C₆₀ (I _h) in its ground electronic state (X ¹A_g) were investigated with density functional theory at B3PW91/6-31G level via structure distortions. The elastic properties were obtained from the potential energy curves (PECs) in all of the five independent distortional directions of the molecule with symmetries of 1. D _5d, 2. D _3d, 3. D _2h, 4. C _2h(1) and 5. C _2h(2). PECs were examined where the structure of Ne@C₆₀ was destroyed. The necessary energies to destroy the structure were thus obtained, which illuminated the stability of Ne@C₆₀. PECs were found to be anisotropic and were accurately fitted to polynomials. Elongations in the direction of D _5d and compression in D _2h encountered potential energy surface cross-linkages, which might be considered as a single electron pump for further application in the design of single electron devices. Time-dependent B3PW91/6-31G analysis predicted significant electronic spectra changes associated with structure distortions. Similarities and differences of the properties were compared with those in C₆₀ and He@C₆₀.     

Electron paramagnetic resonance parameters and local structure for Gd3+ in KY3F10

The electron paramagnetic resonance parameters, zero-field splittings (ZFSs) b₂⁰, b₄⁰, b₄⁴, b₆⁰, b₆⁴ and the g factors for Gd³⁺ on the tetragonal Y³⁺ site in KY₃F₁₀ are theoretically studied from the superposition model for the ZFSs and the approximation formula for the g factor containing the admixture of the ground ⁸S_7/2 and the excited ⁶L_7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions, respectively. By analysing the above ZFSs, the local structure information for the impurity Gd³⁺ is obtained, i.e., the impurity-ligand bonding angles related to the four-fold (C₄) axis for the impurity Gd³⁺ center are found to be about 0.6° larger than those for the host Y³⁺ site in KY₃F₁₀. The calculated ZFSs based on the above angular distortion as well as the g factors are in reasonable agreement with the observed values. The present studies on the ZFSs and the local structure would be helpful to understand the optical and magnetic properties of this material with Gd dopants.