笼状团簇Mg12B24结构与性质的密度泛函理论研究

运用杂化密度泛函B3LYP方法,在6-31G*水平上优化得到了一种Mg₁₂B₂₄团簇的笼状稳定结构,其IR最强吸收峰位于205.23 cm^-1,Raman谱的最强峰位于242.63 cm^-1. Mg₁₂B₂₄团簇笼状结构中B原子主要是sp杂化轨道参与成键,Mg原子主要是s轨道参与成键.团簇中B原子层堆积了大量的电子,表明MgB₂的超导作用主要发生在B原子层;B原子层电子存在较强的离域性,也为超导电性提供了条件;Mg原子起了提供电子的作用.     

笼状Au团簇的休克尔模型研究

这篇文章分别用简单和扩展休克尔模型处理四种具有较大尺寸的笼状Au团簇(Au32,Au42,Au50,Au72),这四种团簇经理论计算预言具有较高的稳定性. 将两种休克尔模型计算得到的能级分布,最高占据分子轨道(HOMO)与最低未占据分子轨道(LUMO)之间能隙,以及平均结合能与密度泛函理论的计算结果进行比较,探讨了采用休克尔模型研究笼状Au团簇的适用性,进而讨论了这些笼状团簇的球形芳香性.     

笼状金团簇的休克尔模型研究

这篇文章分别用简单和扩展休克尔模型处理四种具有较大尺寸的笼状Au团簇（Au32,Au42,Au50,Au72）,这四种团簇经理论计算预言具有较高的稳定性. 将两种休克尔模型计算得到的能级分布,最高占据分子轨道(HOMO)与最低未占据分子轨道（LUMO）之间能隙,以及平均结合能与密度泛函理论的计算结果进行比较,探讨了采用休克尔模型研究笼状Au团簇的适用性,进而讨论了这些笼状团簇的球形芳香性.     

(HgSe)_n(n=1～6)团簇结构和性质的密度泛函研究

本工作采用LANL2DZ赝势基组、B3LYP方法对(HgSe)n(n=1~6)团簇进行了结构优化、自然键原子轨道和频率计算,得到(HgSe)n(n=1~6)团簇基态的平衡几何结构、电子状态、垂直电离势、垂直电子亲和势、偶极矩、三个基本热力学函数等相关性质,并系统分析了该团簇的几何构型、原子净电荷布局、前沿分子轨道特征.结果表明:基态稳定结构(HgSe)2为平面四边形,(HgSe)n(n=3~6)为笼状结构,且稳定顺序为(HgSe)5(HgSe)4(HgSe)6(HgSe)2HgSe(HgSe)3,极性顺序为:(HgSe)4HgSe(HgSe)3(HgSe)5(HgSe)6(HgSe)2,(HgSe)6和(HgSe)2分子空间结构的对称性较好.(HgSe)n(n=1~6)团簇各体系都有较好的电子供体及受体等活性部位,随着n增大轨道离域现象明显,利于电子的转移,导电性增强.     

B12N12纳米笼：潜在的二氧化氮检测传感器

利用密度泛函理论通过计算吸附能量、HOMO/LUMO能隙变化、电荷转移、结构扭曲等研究二氧化氮分子在B12N12纳米笼的吸附．此外,通过计算B₁₂N₁₂的电子结合能、Gibbs自由能、态密度和分子表面的静电势研究其稳定性和其它特性．B₁₂N₁₂纳米笼吸附二氧化氮显示三种构型．B₁₂N₁₂团簇的HOMO/LUMO能隙变化对二氧化氮分子的存在非常敏感,从自由团簇的6.84 eV降为NO₂/团簇稳定团簇的3.23 eV．团簇的导电性被极大地提高,表明B₁₂N₁₂纳米簇可能是潜在的二氧化氮气体分子检测传感器.     

AgGe_n(n=1～17)团簇:几何结构,稳定性和电子性质

利用密度泛函理论的B3LYP/LanL2DZ方法,对AgGe_n(n=1～17)团簇进行了系统的研究,较小的AgGe_m(n=1～11)和相对较大的AgGe_n(n=12～17)团簇出现了不同的生长方式.从n=12开始,形成了银原子被锗原子完全包围的笼状结构.根据AgGe_n团簇的分裂能和二阶能量差分,预测了AgGe_n(n=1～17)团簇的幻数为n=5、10、12和15.Mulliken电荷布局分析显示电荷转移的方向和团簇的大小与掺杂的金属种类有关.通过分析振动光谱,研究了团簇的动态稳定性,在实验中明显的红外谱和拉曼谱能被用来区别团簇结构.     

InnAsn (n=1-20)小团簇几何结构与电子性质的第一性原理研究

基于密度泛函理论的第一性原理方法,采用B3LYP下的赝势基组LanL2DZ,研究了InnAsn (n=1-20)团簇的基态几何结构、相对稳定性、电子性质及其振动光谱. 结果表明,当n=5-11时团簇的基态构型为层状结构; 当n=12-20时团簇的基态构型为笼状结构. 团簇平均结合能、二阶能量差分和HOMO-LUMO能隙均在n=9,12,18出现极大值,说明In9As9、In12As12和In18As18为幻数团簇. 另外,HOMO-LUMO能隙的计算结果表明InnAsn (n=1-20)团簇具有宽带隙半导体特征.     

磁控溅射法制备金团簇纳米颗粒及性能表征

 采用磁控溅射法制备金团簇纳米颗粒，用透射电镜(TEM)、X射线衍射(XRD)、紫外可见光分光光度计(UV-Vis)和X射线光电子能谱(XPS)等分析手段对其表征，研究了金团簇纳米颗粒的形貌、颗粒度、结构、光吸收性质及物质成份。研究结果表明：制备的金团簇纳米颗粒呈球形，平均粒径在10 nm左右，粒径分布均匀，无团聚、氧化现象，颗粒的结构为面心立方。在519 nm处出现团簇颗粒的表面等离子共振吸收峰，测试得到Au(4f_7/2)和Au(4f_5/2)电子的结合能分别为83.3 eV和86.9 eV，并且没有出现金的氧化产物。     

过渡金属原子钴掺杂硅团簇CoSi6-9的密度泛函理论研究

利用密度泛函理论对CoSin(n=6-9)中性团簇的几何结构演化和电子结构性质进行研究,结果表明Co掺杂硅团簇的最小笼状尺寸是n=9,其中Co原子被扭曲状的Si9棱柱包拢。CoSi8团簇由于存在多个能量相近的异构体,导致团簇的吸附活性降低。自然电荷布局分析表明对于笼状的Co@Si9团簇,其电荷主要分布在外围的硅笼,内部的Co原子通过spd杂化与外部硅笼成键,这保持了笼状团簇的稳定。     

过渡金属原子钴掺杂硅团簇CoSi6-9的密度泛函理论研究

利用密度泛函理论对CoSin(n=6-9)中性团簇的几何结构演化和电子结构性质进行研究,结果表明Co掺杂硅团簇的最小笼状尺寸是n=9,其中Co原子被扭曲状的Si9棱柱包拢。CoSi8团簇由于存在多个能量相近的异构体,导致团簇的吸附活性降低。自然电荷布局分析表明对于笼状的Co@Si9团簇,其电荷主要分布在外围的硅笼,内部的Co原子通过spd杂化与外部硅笼成键,这保持了笼状团簇的稳定。     

B80 fullerene: an Ab initio prediction of geometry, stability, and electronic structure

The geometry, electronic, and structural properties of an unusually stable boron cage made of 80 boron atoms are studied, using ab initio calculations. The shape of this cluster is very similar to that of the well-known C60 fullerene, but in the B80 case, there is an additional atom in the center of each hexagon. The resulting cage preserves the Ih symmetry, has a relatively large highest occupied and lowest unoccupied energy gap ( approximately 1 eV) and, most importantly, is energetically more stable than boron double rings, which were detected in experiments and considered as building blocks of boron nanotubes. To our knowledge, this is the most stable boron cage studied so far.     

AlH(3) and Al(2)H(6): magic clusters with unmagical properties

Enhanced stability, low electron affinity, and high ionization potential are the hallmarks of a "magic" cluster. With an electron affinity of 0.28 eV, ionization potential of 11.43 eV, and a large binding energy, AlH(3) satisfies these criteria. However, unlike other magic clusters that interact only weakly with each other, two AlH(3) clusters bind to each other with an energy of 1.54 eV. The resulting Al(2)H(6), while also a magic cluster in its own right, possesses the most unusual property that the difference between its adiabatic and vertical detachment energy is about 2 eV--the largest of any known cluster. These results, based on density functional theory, are verified experimentally through photodetachment spectroscopy.     

Enhanced optical nonlinearity based on silicon ring

The photoelectron spectrum of ethylene is studied using coupled cluster methods, including an existing ambiguity in what are reported to be its experimental vertical ionization potentals. Two complementary methods are used for generating the ionization potentials: δE CCSD(T) and IP-EOM-CCSD. The adiabatic IP of the neutral molecule in the ground state is well known and widely accepted to be 10.5122eV. The basis set extrapolated adiabatic IPS with zero-point corrections are 10.46 eV and 10.56 eV, respectively, but a vibronic coupling between the ground state cation and its first excited state can reduce these values by ～0.03 eV. From an exponential basis set extrapolation the vertical ionization potentials are predicted to be 10.8 eV (B_3u, 13.2eV (B_3g 15.0eV (A_g), 16.4eV (B_2u), and 19.6eV (B_1u) ±0.1 eV.     

New detecting system of the NEVOD Cherenkov water detector

A new detecting system of the NEVOD Cherenkov water detector is described, whose development implies replacement of photomultipliers in quasispherical modules of the existing three-dimensional network by low-noise FEU-200 photomultipliers, their dynamic range expansion with the purpose to study events with energies above 10¹⁷ eV, the transition to the cluster structure principle, and the possibility of operating in the hodoscopic mode.     

High inertness of W@Si12 cluster toward O2 molecule

The geometry, electronic structure, and reactivity with O₂ molecules of an isolated W@Si₁₂ cluster have been investigated by first principles simulations. The results confirm that O₂ can weakly adsorb on the HP-W@Si₁₂ cage with a binding energy of 0.004 to 0.027 eV. O₂ may dissociate on the cluster by overcoming energy barrier of at least 0.593 eV. However, this is a spin-forbidden reaction, rendering the high inertness of the HP-W@Si₁₂ cluster toward O₂. These results confirm the high inertness of the W@Si₁₂ cluster toward O₂ molecules in ambient conditions, in close agreement with experimental observations of magic cluster of W@Si₁₂.     

Charge-transfer transitions and optical spectra of vanadates

Specific features of the charge-transfer states and O2p → V3d transitions in the (VO₆)^9? octahedral complex are studied using the cluster approach. The reduced matrix elements of the electric-dipole transition operator are calculated for many-electron wave functions corresponding to the initial and final states of a charge-transfer transition. Using a parameterization of the results, the relative intensities of the allowed charge-transfer transitions are calculated disregarding the mixing of different configurations of the same symmetry. The Tanabe-Sugano theory is used with inclusion of this mixing to calculate the energies of many-electron charge-transfer transitions and their actual intensities. Modeling of the optical spectrum of LaVO₃ reveals a complicated charge-transfer transition band consisting of 81 lines. The main maxima of the band are in the range 6.3–7.3 eV. There are also additional maxima in the regions of ≈3 and ≈8–9 eV. The bandwidth is ≈10 eV. The results of model calculations are in agreement with experiments and demonstrate the weakness of the widely used assumption that the spectrum of charge-transfer transitions has a simple structure.     

Electronic structure of solid C48N12 aza-fullerene

I report electronic structures and the cohesive energy for face-centered-cubic (fcc) solid C₄₈N₁₂ using generalized-gradient density-functional theory. The full vibrational spectrum of the C₄₈N₁₂ cluster is calculated within the harmonic approximation at the B3LYP/6-31G* level of theory. The results show that fcc is energetically preferred and a more stable crystal form than body-centered-cubic (bcc). C₄₈N₁₂ clusters are found to condense by a weak (0.29 eV) van der Waals force. The band gap of fcc C₄₈N₁₂ is calculated to be 1.3 eV at the GGA-PW91 level, whereas the HOMO-LUMO gap is calculated to be 2.74 eV using B3LYP/6-31G*.     

Restoration of parameters of high-energy cascades in Cherenkov water calorimeter with a dense array of quasispherical modules

A problem concerning the restoration of the parameters of a cascade shower with an unknown axis originating by muons in a Cherenkov water calorimeter is considered. A method for estimating the direction and geometric position of the cascade’s axis, which is based on the analysis of responses of quasispherical modules, and the criteria of selection of the events with cascades among the events with a large energy liberation are proposed. The method and the criteria are tested on events with cascades generated by near-horizontal muons of high energies detected by a DECOR coordinate-track detector. The preliminary results of measurements of the energy spectrum of cascade showers are presented.     

Photoexcitation of a volume plasmon in C60 ions

Neutral C60 is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for C+60, C2+60, and C3+60 ions in the 17-75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.