NaBn(n=1—9)团簇的几何结构和电子性质

应用密度泛函理论(DFT)中B3LYP方法在6-311+G(d)水平上计算并分析了 NaB_n(n=1—9)团簇的几何结构及电子性质. 同时, 讨论了团簇的平均结合能、能级间隙、二阶能量差分和极化率.研究表明:NaB_n(n=1—9) 团簇基态绝大多数为平面构型. 能级间隙和二阶能量差分结果表明NaB₃与NaB₅是幻数团簇. 另外, 对平均线性极化率和极化率的各向异性不变量研究表明基态NaB_n团簇的电子结构随B原子的增加虽然趋于紧凑, 但尚未形成特定的堆积方式.     

Density Functional Theory Study on Electronic and Magnetic Properties of Mn-doped (MgO)n (n=2～10) Clusters

利用密度泛函理论方法优化了纯的和M_n原子掺杂的(MgO)_n (n=2～10)团簇的几何结构. 在Mn原子掺杂的氧化镁结构中, 获得了一系列的同分异构体和与之相对应的总能量.MnMg_n-1O_n(n=2～10)的几何构型显示Mn原子优先取代低配位的Mg原子. 结构稳定性分析表明,除了(MgO)₁₀团簇外,其它纯的和掺杂结构的平均结合能均随着团簇的增大而增强. MnMg_n-1O_n团簇的二阶能量差结果表明MnMg₅O₆和MnMg₈O₉比相邻的团簇表现出更高的相对稳定性. 除了MnMgO₂团簇的磁矩为3.00 μB外,其它掺杂结构的磁矩均为5 μB左右. 它们的磁性主要受电荷转移大小、原子在结构中的位置以及结构尺寸所影响.     

4s和4p半核态引入价态(导致杂化指数降低)可以减弱Mo_n(n=2～18)团簇的二聚体现象的第一性原理研究（英文）

钼团簇因具有独特的结构、电子和物理化学性质,被期待在未来的纳米科技中扮演重要角色,但是它们的基态结构至今还存在争议.本研究采用粒子群优化(CALYPSO)方法对Mo_n(n=2～18)团簇的晶体结构进行全局域能量最小化搜索,并结合第一性原理方法进一步优化.计算表明:当4s和4p半核态不作为价态时,Mo_n(n=2～18)团簇有明显的二聚体趋势,原子数为偶数的团簇往往是"幻数"团簇,具有较高的稳定性;但是,将4s和4p电子作为价电子后,平均杂化指数H_(sp)、H_(sd)和H_(pd)显著降低,二聚体趋势急剧减弱.本文报道了Mo_n(n=11,14,15)团簇的新基态结构,证明了半核态对于Mo_n团簇是十分重要的.     

HC2nO+ (n=3-6) 正离子的红外光解离光谱以及理论计算研究

本文利用脉冲激光溅射-超声分子束载带离子源在气相中产生了HC_2nO⁺ (n=3-6)正离子. 通过对贴附CO的络合物离子的红外光解离光谱实验获得了HC_2nO⁺正离子在1600∽3500 cm^-1范围内的红外光谱. 通过比较实验光谱和理论模拟光谱确定了HC_2nO⁺正离子具有端接氢和氧的直线型碳链衍生物结构,基态为三重态,单重态比三重基态能量高10∽15 kcal/mol. 成键分析表明HC_2nO⁺中的碳链具有连烯的结构特征.     

AlnC4-/0(n=2∽4)团簇的结构和成键性质: 光电子能谱和理论计算

本文采用尺寸选择的负离子光电子能谱与高精度理论计算,对Al_nC₄^-/0(n=2∽4))团簇的结构和成键性质进行了研究. Al₂C₄^-团簇负离子的最稳定结构是一个C_2v对称的平面结构,其中两个C₂单元与两个铝原子分别相连. Al₂C₄^-团簇负离子的次稳定结构是一个线型结构,两个铝原子位于C₄线型结构两端,能量仅比最稳定结构高0.05 eV. 中性Al₂C₄团簇是一个线型结构. Al₃C₄^-团簇负离子是一个平面结构,其中三个铝原子分别与两个C₂单元相连. 而中性Al₃C₄团簇则是一个V字型结构. Al₄C₄^-团簇负离子和中性Al₄C₄团簇均为C_2h对称的平面结构,四个铝原子分别位于两个C₂单元的末端. Al_nC₄^-/0(n=2∽4))团簇负离子的自适应自然密度配分的分析结果表明这些团簇中铝原子与C₂单元之间的化学键具有σ和π键特征.     

小尺寸VmOn+团簇的激光光解和密度泛函计算

通过激光溅射法产生了V₂O_n⁺ (n=1, 2), V₃O_n⁺ (n=1, 2, 3)和V₄O₃⁺等缺氧的钒氧团簇,并采用532和266 nm波长的激光对它们进行了光解研究. 利用密度泛函理论计算与激光光解实验相结合确定了这些团簇的几何结构和可能的光解通道. 激光光解实验表明V相似文献   

[Co(CO2)n]+团簇的红外解离光谱实验和理论研究

本文利用红外光解离光谱研究了一价钴阳离子与二氧化碳之间的相互作用. 通过密度泛函理论计算得到[Co(CO₂)_n]⁺团簇的几何结构,并且模拟了它们的振动光谱与实验数值进行比较. 研究结果表明,在[Co(CO₂)_n]⁺(n=2∽6)团簇中,钴阳离子通过电四极矩静电作用以端点结合的方式与二氧化碳中的氧原子结合在一起. 团簇的红外光谱都集中在二氧化碳反对称伸缩的波数附近,并且随着团簇尺寸的变化出现蓝移,最后把[Co(CO₂)_n]⁺的红外光解离光谱与稀有气体贴附的[Co(CO₂)_n]⁺-Ar的红外光解离光谱进行了比较.     

ConCm±(n=1-5; m=1,2)团簇的密度泛函理论研究

本文采用基于自旋极化的密度泛函理论系统研究了Co_nC_m^± (n=1-5; m=1,2)团簇的几何结构和电子结构特性. 将Co_nC^± (n=2-5)团簇中的一个Co替换为C原子, 个体的基态几何结构发生明显变化; 在Co_nC₂^± (n=1-5)团簇的生长序列中, 发现从n=3开始团簇中的两个C原子有彼此分离分布的趋势, 我们分析, 这是Co金属能够维持单壁碳纳米管(SCNTs)保持开口生长, 成为非常有效的一种催化剂的重要原因. 同时, 将Co_nC^± (n=2-5)团簇中添加一个Co原子后系统的总磁矩出现大幅下降的趋势, 但仍保持奇偶交替的规律. 通过比较中性及带电的Co_nC以及Co_nC₂ (n=1-5)团簇的碎裂能, 本工作发现: 由实验获取的SCNTs应均为带正电的体系, 这一结论与已有的实验模型拟合得很好.     

TiGen-(n=7~12)团簇的光电子能谱及密度泛函理论研究

利用光电子能谱及密度泛函理论计算对TiGe_n^-(n=7~12)团簇的几何结构及电子特性等进行了系统研究. 对于TiGe_n^-负离子及中性TiGe_n,在n=8时出现了钛原子半内嵌的船型结构;在n=9~11时,新增的锗原子加盖到这种船型结构上,逐步形成钛原子完全内嵌的结构. TiGe₁₂^- 团簇具有一种钛原子内嵌的变形六棱柱结构. 自然布居分析结果显示,对于n=8~12的TiGe_n^-/0 团簇,随着内嵌结构的形成,有电子从锗原子转移到钛原子,说明其电荷转移方式与结构演变密切相关.     

第一性原理计算ZrnFe(n=2—13)团簇的基态结构及其磁性

从第一性原理出发，利用密度泛函理论中的广义梯度近似对Zr_nFe(n=2—13)团簇进行了结构优化、能量和频率计算.在充分考虑自旋多重度的前提下，对每一具体尺寸的团簇，得到了多个平衡构型，并根据能量高低确定了团簇的基态结构.综合团簇的结合能、二阶能量差分以及团簇的最高占据轨道和最低未占据轨道间的能隙可知Zr₅Fe，Zr₇Fe和Zr₁₂Fe团簇的稳定性相对较高，Zr₁₂Fe团簇的结构是具有I_h对称性的正二十面体，而且Zr₁₂Fe的稳定性在所有团簇中是最高的.另外，不仅Zr₅Fe，Zr₇Fe和Zr₁₂Fe团簇的稳定性相对较高，而且它们均为磁性团簇(而Zr_n团簇的磁矩在n≥5时已经发生了淬灭)，由此可知通过选择合适的掺杂元素可能得到高稳定的磁性团簇.从Mulliken布居分析结果可知，除了在Zr₁₂Fe团簇中Fe原子失去少量电荷外，其他团簇中Fe原子均从Zr原子那里得到了一定量电荷，即Fe原子在Zr_nFe(n=2—13，n≠12)团簇中是电子受体.     

Pt_nAl(n=1—8)小团簇的密度泛函理论研究

采用密度泛函理论方法,在BPW91/LANL2DZ水平下详细研究了Pt n Al(n=1—8)团簇的几何结构、稳定性和电子性质.同时,分析了团簇的结构演化规律、平均结合能、二阶能量差分、能隙、磁性、Mulliken电荷和电极化率.结果表明:除Pt2Al外,所有Pt n Al(n=1—8)团簇的基态几何结构都可以用Al原子替换Pt n+1基态构型中的Pt原子得到,且Al原子位于较高的配位点上.二阶能量差分、能隙的分析结果表明,PtAl和Pt4Al团簇相对其他团簇具有较高的稳定性.Mulliken电荷分析表明,Al原子所带的电荷转移到Pt原子上,Al原子是电荷的捐赠者.磁性的分析说明,单个Al原子的加入对Pt n团簇的平均每原子磁矩随尺寸的变化趋势没有影响,但总体上降低了Pt n团簇的平均磁矩.极化率的研究表明,富Pt团簇的非线形光学效应强,容易被外场极化.     

Role of semicore electrons in the lattice dynamics of a cubic ZnS crystal

The phonon dispersion in a ZnS crystal has been studied by the density functional theory method with different pseudopotentials containing 10 (Zn¹²⁺) and 18 (Zn²⁰⁺) semicore electrons of the shell with the principal quantum number n = 3 in a zinc atom. It has been found that the pseudopotential of Zn²⁰⁺, unlike the pseudopotential of Zn¹²⁺ describes the phonon dispersion more accurately. An analysis has demonstrated that, in this case, the degree of d-p hybridization of semicore d states of zinc with the valence p states of sulfur decreases.     

Structures and electronic properties of Mo2nNn（n=1-5）:a density functional study

The lowest-energy structures and the electronic properties of Mo2nNn(n=1-5) clusters have been studied by using the density functional theory(DFT) simulating package DMol 3 in the generalized gradient approximation(GGA).The resulting equilibrium geometries show that the lowest-energy structures are dominated by central cores which correspond to the ground states of Mo n(n = 2,4,6,8,10) clusters and nitrogen atoms which surround these cores.The average binding energy,the adiabatic electron affinity(AEA),the vertical electron affinity(VEA),the adiabatic ionization potential(AIP) and the vertical ionization potential(VIP) of Mo2nNn(n=1-5) clusters have been estimated.The HOMO-LUMO gaps reveal that the clusters have strong chemical activities.An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with cluster size.     

Investigations of the Spin-Hamiltonian Parameters for the Rhombic Mo5+ Centers in Ca1−x Y x MoO4 Crystal

The spin-Hamiltonian parameters (g factors g _i and hyperfine structure constants A _i , where i = x, y, z) of the rhombic Mo⁵⁺ center in Ca_1?x Y _x MoO₄ crystal are calculated from the high-order perturbation formulas based on the two-mechanism model for the rhombic d¹ tetrahedral clusters with the ground state |d _z 2〉. In these formulas, besides the contributions due to the widely applied crystal-field (CF) mechanism concerning CF excited states, those due to the charge-transfer (CT) mechanism (which is omitted in CF theory) concerning CT excited states are considered. The calculated results are in reasonable agreement with the experimental values. The calculations show that because of the great relative importance of CT mechanism for the components of spin-Hamiltonian parameter along x and y axes, the accurate and complete calculations of spin-Hamiltonian parameters for Mo⁵⁺ and other high valence state dⁿ ions in crystals should take account of both the CF and CT mechanisms. The defect model of the rhombic Mo⁵⁺ center is also confirmed from the calculations.     

Time-dependent density functional theory study on electronic excited states of the hydrogen-bonded solute-solvent phenol-(H2O)n (n=3-5) clusters

The solute-solvent interactions of hydrogen-bonded phenol-(H₂O)_n (n=3-5) clusters in electronic excited states were investigated by means of the time-dependent density functional theory (TDDFT) method. The geometric structures and IR spectra in ground state, S₁ state, and T₁ state of the clusters, were calculated using the density functional theory (DFT) and TDDFT methods. Only the ring form isomer, the most stable one of the cluster, was considered in this study. Four, five and six intermolecular hydrogen bonds were formed in phenol-(H₂O)₃, phenol-(H₂O)₄, and phenol-(H₂O)₅ clusters, respectively. Based on the analysis of IR spectra, it is revealed that the “window region” between unshifted and shifted absorption bands in both S₁ and T₁ state becomes broader compared with that in ground state for the corresponding clusters. Furthermore, two interesting phenomenon were observed: (1) with the anticlockwise order of the ring formed by the intermolecular hydrogen bonds in the H-bonded phenol-(H₂O)_n (n=3-5) clusters, the strengths of the intermolecular hydrogen bonds decrease in all the S₀, S₁ and T₁ states; (2) upon electronic excitation, the smaller the distance between phenol and water is, the larger the change of intermolecular hydrogen bonds strength is. Moreover, the intermolecular hydrogen bond (phenolic OH is the H donor) is strengthened in excited state compared with that in ground state. But the intermolecular hydrogen bond (phenolic OH is the H acceptor) is weakened in excited state.     

Infrared ion dip and ultraviolet spectroscopy of 4-phenyl imidazole, its tautomer, 5-phenyl imidazole, and its multiply hydrated clusters

Mass-resolved resonant two photon ionisation (R2PI) and infrared ion dip spectra have been recorded for 4-phenylimidazole (4PI) and its singly and multiply hydrated clusters 4PI(H₂O)_{n = 0 - 4}, under supersonic expansion conditions. In the case of 4PI(H₂O)_0,1, it has also been possible to record infrared spectra in both the ground (S₀) and excited (S₁) states. Combining the experimental data with the results of ab initio calculations has led to the structural assignment of each cluster. In each case, the water molecules bind primarily to the NH site of the imidazole ring. Clusters with n≥ 2 incorporate linear water chains, in which the proton donating terminus bridges either to the π-electron system (n = 2) or to the >N: atom site (n = 3, 4) on the imidazole ring. Despite the creation of a “water wire”, connecting the donor and acceptor sites of imidazole, there is no evidence of proton transfer in either the ground or excited state. Received 20 December 2001 Published online 13 September 2002     

三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

Structures,stabilities and adsorption mechanisms of nitrogen adsorbed on Mon (n = 1–8) clusters

Configurations, stabilities and adsorption mechanisms of ground-state Mo_nN and Mo_nN₂ (n?=?1–8) clusters are calculated by using the density functional method within the PBE level. Evidently, N atoms tend to approach more Mo atoms. Doping with two N impurity prefers to occupy symmetrical position of the host Mo_n (n?=?1–8) cluster except for Mo₂N₂ clusters. Mo₄N, Mo₆N, Mo₂N₂, Mo₄N₂ and Mo₆N₂ clusters have higher structural stabilities than their neighbors by the second derivative of total binding energy. Mo₂N, Mo₄N and Mo₇N, Mo₂N₂, Mo₅N₂ and Mo₇N₂ clusters have higher kinetic reactivity than their neighbors by the HOMO–LUMO gaps. The adsorption capacity of a N atom to Mo₄ cluster is stronger than the other Mo–N clusters.     

幻数尺寸Li-n-1,Lin,Li+ n+1(n=20,40)团簇的几何结构、电子与光学性质的第一性原理研究

基于密度泛函理论,采用第一性原理分子动力学模拟退火方法,对Li^-_n-1,Li_n,Li⁺_n+1 (n=20,40)的最低能量结构进行了全局搜索. 发现锂团簇的生长模式是以单个或多个嵌套的正多面体为核心,其余原子以五角锥为基本单元围绕核心生长. 基于最低能量结构的第一性原理电子结构计算得到锂团簇的分子轨道能级分布与无结构凝胶模型给出的电子壳层完全一致. 在总电 关键词： 团簇 电子结构 极化率 光吸收     

Some exact results for the spin-1/2 Falicov-Kimball model in the strong coupling limit

The spin-1/2 Falicov-Kimball model for electronically driven valence and metal-insulator transitions is studied analytically using strong-coupling perturbation theory. It is shown that in the limit of the infinite interaction strength between localized and itinerant electrons the Falicov-Kimball model undergoes two types of discontinuous valence transitions: the insulator-metal transitions from an integer-valence ground state (n _f = 1) into an inhomogeneous intermediate-valence ground state (0 < n _f < 1) and the insulator-metal transitions from n _f = 1 to n _f = 0. In addition, we discuss the role of the electron-phonon interaction on the mechanism of valence transitions and we present possible extensions of the exact one dimensional results to higher dimensions.