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.     

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.     

甲基铝氧烷纳米管分子结构的理论研究

用密度泛函理论对[(AlOMe)₂]_n、[(AlOMe)₃]_n和[(AlOMe)₄]_n (n=1～10)作为重复单元组成的甲基铝氧烷(MAO)纳米管进行了研究,计算了其所有体系的结合能和总能量．结果表明,[(AlOMe)₃]_n和[(AlOMe)₄]_n具有稳定的纳米管结构,在所有研究系统中n=3时具有最稳定的结构．考察发现,[(Al₅O₅)]_n和[(Al₇O₇)]_n两种结构的二聚体具有无规则、扭曲的结构,不能继续增长形成纳米管结构．     

Al2O3Hx(x=1—3)分子团簇的结构与光谱研究

用密度泛函理论(DFT)的B3lyp方法在6-311++g(d,p)水平上对Al₂O₃H_x(x=1—3)分子的几何构型, 电子结构, 振动频率等性质进行了系统研究. 并给出了它们可能基态结构的总能量(E_T), 零点能(E_z), 摩尔热容(C_v), 标准熵(S), 原子化能(ΔE_m), 垂直电离能(IP)及垂直电子亲和能(E_A). Al₂O₃H和Al₂O₃H₂分子可能的基态的几何构型都为平面结构. Al₂O₃H₃的两个可能为基态的几何构型都是在立体Al₂O₃(D_3h)的几何结构基础上加三个氢原子构成. 这三个分子的能量最低结构为Al₂O₃H(²A′)C_s, Al₂O₃H₂(¹A′) C_s, Al₂O₃H₃ (²A) C₁.     

C80H80几何结构和电子性质的密度泛函研究

采用密度泛函理论方法中的广义梯度近似,对C₈₀H₈₀几何结构和电子性质进行了研究. 几何结构研究表明:在C₈₀H₈₀可能稳定存在的两种同分异构体中, 连接12个五边形的20个C原子内部氢化,其余60个C原子外部氢化所形成的结构即 H₂₀@C₈₀H₆₀最稳定,其仍然保持I_h对称性. 通过对H₂₀@C₈₀H₆₀的能级、前线轨道和态密度分析可知: 在H₂₀@C₈₀H₆₀中, H原子的原子轨道与C原子的原子轨道之间在占据态轨道上有较强的杂化, H原子对H₂₀@C₈₀H₆₀的占据态轨道的贡献比较大. 其最高占据轨道主要由外部H原子和碳笼来贡献,而最低未占据轨道主要由内部H原子贡献, 表明内外H原子在H₂₀@C₈₀H₆₀的化学反应中承担不同的角色. H₂₀@C₈₀H₆₀为闭壳层结构,所有电子都是配对的,表现为非磁性.     

π-(C5H5)2TiCl2·AlR3系可溶性催化剂的电子自旋共振波谱

本文稿研究了Al(iC₄H₉)₃、Al(C₂H₅)₃、Al(C₂H₅)₂Cl、Al(C₂H₅)Cl₂等与π-(C₅H₅)₂TiCl₂所形成的络合物在无溶剂以及在溶剂稀释过程中的电子自旋共振波谱。根据实验结果,作者认为未成对电子是定位在Al²⁷核一端,电子云可延伸到α氢原子位置上,并指出溶剂主要起着分散络合物的作用。     

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.     

AunSc (n=2～13)团簇的第一性原理研究

采用密度泛函理论中的广义梯度近似(GGA)对Au_nSc(n=2～13)的几何构型进行优化,并对能量和电子性质进行了计算．结果表明,当n≤11时,Au_nSc的低能量结构是平面结构,且掺杂的Sc原子没有扰乱Au_n的框架;当n≥12,Sc原子陷入了金团簇所形成的笼内．二阶能量差分、分裂能、电离势、亲和势和能隙表明Au₃Sc、Au₅Sc、Au₇Sc、Au₉Sc、Au₁₁Sc和Au₁₃Sc是较稳定的团簇;掺杂的Sc原子提高了纯金团簇的稳定性且改变了纯金团簇化学活性的;当n≤11时,Au_nSc的磁矩在0.000～1.000 μB振荡;对于n≥12,Au_nSc的磁矩出现了猝灭．     

密度泛函理论对ZrnPd团簇结构和性质的研究

用B3LYP/LANL2DZ方法对Zr_nPd(n =1—13)团簇的平衡几何结构、能量、频率、电子性质和磁性进行了计算.研究表明,Pd原子位于表面的异构体更为稳定,其中Zr₇Pd,Zr₁₂Pd团簇稳定性高,是幻数团簇,此外,相对于Zr_nCo与Zr_nFe团簇,Zr_nPd团簇参与化学反应的能力较弱,化学稳定性更     

AuCn-/0 (n=3-8)的负离子光电能谱和密度泛函理论研究：电子结合能和几何结构的奇偶效应

本文测量了AuC_n^- (n=3-8)的光电子能谱,并且对AuC_n^-/0 (n=3-8)的结构和性质进行了理论研究. 研究发现,AuC_n^-的光电子能谱表现出明显的奇偶交替变化,AuC₃^-、AuC₅^-、AuC₇^-的光电子能谱峰明显宽于AuC₄^-、AuC₆^-、AuC₈^-的光电子能谱峰,AuC₃^-、AuC₅^-、AuC₇^-的电子垂直脱附能低于AuC₄^-、AuC₆^-、AuC₈^-的电子垂直脱附能. AuC_n^- (n=3-8)的最稳定结构是链状结构. 在中性团簇AuC_n(n=3-8)中,除了AuC$₃和AuC₅的结构轻微弯曲外,其他团簇均是直线型结构. 理论计算的∠AuCC角度,Au-C键长和Au原子的电荷分布均呈现奇偶变化,与实验观测一致.     

Structures and electronic properties of stoichiometric hydrogenated aluminum clusters

The lowest-energy geometries and electronic-structure properties have been obtained for Al_nH_n (n=1-10) clusters within the density-functional theory using the generalized gradient approximation for the exchange correlation potential. The resulting geometries show that the hydrogen atoms tend to occupy outside positions and no hollow positions are found. The subunit Al_n of Al_nH_n (n=1-5) have little distortion, in comparison with corresponding pure Al_n cluster, whereas the subunit Al_n have large distortion from n=6. The stability has been investigated by analyzing the binding energy per atom and the second difference in energy, indicating that Al₈H₈ exhibit higher stability than others. The bonding property has been analyzed by calculating the Mulliken charges and Al–H distances. The calculated energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), the vertical ionization potential, and the vertical electron affinity also confirm that Al₈H₈ is a stable cluster. The density of states (DOS) shows that Al_nH_n exhibit changes from molecular-like (Al₁H₁) to band-like structure (Al₁₀H₁₀) as n increases.     

关于Al_nC和Al_nC~+(n=1—8)团簇结构和稳定性的研究

通过采用7种密度泛函理论DFT方法对AlnC进行计算,所得结果与实验数据比较,选择了B3lyp方法和6-311G(d)基组对AlnC及AlnC+(n=1—8)团簇进行结构优化和频率分析,得到了AlnC及AlnC+基态以及亚稳态结构.当n从小到大变化时,这些团簇的结构从平面向立体过渡,平面构型以三角形为主,立体构型主要是三棱柱笼状结构;在这些团簇中的高对称性结构中,中性团簇和阳离子只能有其一是稳定构型;在所研究的团簇中,Al2C和Al5C团簇较为稳定.     

Isotope effect and cluster size dependence for water and hydrated hydrogen halide clusters: multi-component molecular orbital approach

In order to explore the proton/deuteron (H/D) isotope effect on the structures, wavefunctions, and size dependence of water clusters, both electronic and nuclear wavefunctions are determined simultaneously. The optimized centres and the exponents for the nuclear orbitals indicate the Ubbelohde effect, i.e. the deuteron has weaker hydrogen bonding than the proton. Calculations are made also of hydrogen halide water clusters, Such as HF(H₂O)_n, HB_r(H₂O)_n, (n = 0–4), and their deuterated species. Only the hydrogen transferred ring structure is optimized for the protonic HBr (H₂O)₃ cluster, while both the hydrogen transferred and the non-transferred structures are obtained for the deuterated DBr (H₂O)₃ cluster under the one-particle multi-component treatment. The proton in the HF molecule is localized more than those in the HCl and HBr molecules, and no hydrogen transferred structures are obtained for HF water clusters.     

Isotope effect of hydrated clusters of hydrogen chloride,HCl(H2O) n and DCl(H2O) n (n = 0–4): application of dynamic extended molecular orbital method

The recently proposed dynamic extended molecular orbital (DEMO) method is applied to the HCl(H₂O) _n and DCl(H₂O) _n (n = 0–4) clusters in order to explore the isotope effect on their structures, wavefunctions, and energies, theoretically. Since the DEMO method determines both electronic and nuclear wavefunctions simultaneously by optimizing all parameters including basis sets and their centres variationally, we can get the different nuclear orbitals for proton and deuteron as well as their electronic wavefunctions. The positions of the centres of nuclear orbitals show that the deuteron has weaker hydrogen bonding than the proton. There are three isomers in the case of n = 3 clusters, and less stable isomers have hydrogen transferred and non-transferred structures. In the conventional MO calculation, both hydrogen transferred and non-transferred isomers are calculated to be energy minima. When we have applied the DEMO method, only the hydrogen transferred structure is obtained for HCl(H₂O)₃, while both structures are optimized for DCl(H₂O)₃. Such strong H/D dependence on the structures of the HCl(H₂O) _n and DCl(H₂O) _n clusters can be expressed directly by using the DEMO method. The present application demonstrates that the DEMO method is a useful tool for analysing the anharmonicity and vibronic effects of a hydrogen bonding system.     

Hydrogen storage in boron nitride and carbon clusters studied by molecular orbital calculations

Possibility of hydrogen gas storage in carbon (C) and boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for C₆₀, B₂₄N₂₄ and B₃₆N₃₆ with changing position of hydrogen atom to compare the bonding energy at carbon, nitrogen and boron, tetragonal and hexagonal rings. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bondings with nitrogen atoms and tetragonal rings were the most stable. Stability of H₂ molecules inside BN and C clusters was also investigated by molecular orbital calculations. C and BN clusters showed possibility of hydrogen storage of 6.5 and 4.9 wt%, respectively.     

Density functional study of structural and electronic properties of Al<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>P (2 ≤ <Emphasis Type="Italic">n</Emphasis> ≤ 12) clusters

Low-lying equilibrium geometric structures of Phosphorus-doped aluminum cluster Al _n P (n = 2–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee-Yang-Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated for the ground-state structures within the GGA. It is observed that symmetric structures with the P atom occupying a peripheral position are lowest-energy geometries of Al _n P (n = 2, 4–11), while the P impurities of Al₃P and Al₁₂P prefer to occupy internal sites in the aluminum clusters. Generalized gradient approximation extends bond lengths as compared to the LSDA lengths. The odd-even oscillations in the dissociation energy, the second differences in energy, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within both GGA and LSDA. The stability analysis based on the energies clearly shows the clusters with an even number of valence electrons are more stable than clusters with odd number of valence electrons.     

Theoretical investigation of selected hydrogenated germanium clusters (Ge5Hn,n = 0–12) from density functional theory calculations

ABSTRACT

We reported the selected hydrogen absorption of Ge₅H_n isomers and their Ge₅H_n^? anions in the size range of n?=?0–12 for the first time by B3LYP, BPW91, BHandHLYP and BP86 methods in combination with 6-311++G** basis sets. The optimum geometrical structure, relative stability, electronic properties and dissociation behaviour of Ge₅H_n (n?=?0–12) cluster and their Ge₅H_n^? anions were systematically analysed by a series of methods and can be applied to the study of more complex cluster systems. H bridged structure and double H bridged structures were found in the size range of n?=?1–6 in neutral clusters and corresponding anion with triangular bipyramidal framework of Ge₅. The visible odd-even oscillations were observed in the study of change rules with increasing size from the Δ₂E(n), H-dissociation energy (De), HOMO–LUMO band-gap (E_gap) and electron affinity (EA) energy. This conclusion indicated that Ge₅H_n clusters with even H atoms were more stable than clusters with odd H atoms. The infrared spectra of the Ge₅H_n (n?=?0–12) clusters were also simulated which will further stimulate study on germanium-based nanomaterials.     

The structure and stability of Si@Al<Subscript>12</Subscript>H<Subscript>n</Subscript> (n=1−14) clusters

Density functional theory has been employed in order to investigate the structure and stability of Si@Al₁₂H_n () clusters. Hydrogenated Si@Al₁₂ clusters exhibit pronounced stability for even numbers of H atoms. Large binding energy, HOMO-LUMO gaps and increased ionization potentials imply that these clusters should be physically and chemically stable. The analysis of the charge density of the HOMO plot illustrates that a pair of hydrogen atoms prefer to occupy opposing on-top sites for clusters with an even n number. Studies of deformation charge density plots demonstrate that significant charge transfer occurs from the Si@Al₁₂ to the H atoms.