足球分子的电子结构和UV谱的研究

用INDO/2和INDO/CI方法研究了足球分子的电子结构和UV谱。几何构型优化后得到2种键长:R_(5-6)=1.4507,R_(6-6)=1.3979,相应的键序为1.1356和1.4385。SCF计算得到120个成键轨道和120个反键轨道,符合我们建议的结构规则。足球分子的光谱计算结果是振子强度不为零的跃迁只有一个,其值为386.0 nm,和实测的UV谱符合得较好。     

给体-桥-受体型系列C~6~0吡咯/二茂铁的电子结构及 二阶非线性光学性质的理 论研究

用INDO/2和INDO/CI方法,计算了系列给体-桥-受体(D-B-A)型C~6~0吡咯/二茂铁(C~6~0PY/Fc)的结构和电子光谱,计算结果和实验结果一致,在正确的光谱基础上,用INDO/CI-SOS公式计算了该系列分子的二阶非线性光学系数β~i~j~k,β~μ。考察了分子电子结构对β~μ影响的微观本质。     

给体-桥-受体型系列C~6~0吡咯/二茂铁的电子结构及 二阶非线性光学性质的理 论研究

用INDO/2和INDO/CI方法,计算了系列给体-桥-受体(D-B-A)型C~6~0吡咯/二茂铁(C~6~0PY/Fc)的结构和电子光谱,计算结果和实验结果一致,在正确的光谱基础上,用INDO/CI-SOS公式计算了该系列分子的二阶非线性光学系数β~i~j~k,β~μ。考察了分子电子结构对β~μ影响的微观本质。     

两种C~6~0双炔衍生物的结构、光谱和二阶非线性光学性质的 理论研究

用INDO/2和INDO/SCI方法,计算了C~6~0C(C=CH)~2基态电子结构和电子光谱,所得结果与实验结果基本一致.在此基础上,设计了C60(C=CH)~2,并用同样方法计算了电子结构和光谱.在正确的电子光谱基础上,用ZINDO-SOS方法计算了2个分子的二阶非线性光学系数β~i~j~k和β~μ,并对其结果进行了分析和讨论.结论是,乙炔基与C~6~0(C=CH)~2有更大的非线性光学系数,是有希望的非线性光学备选材料分子。     

卟啉镍分子的激发态和反饱和吸收

用INDO/CI方法研究了卟啉镍分子的电子结构、紫外光谱、激发态,并从理论上指出卟啉镍分子存在反饱和吸收的微观机制.     

两种C60双氰衍生物的结构、光谱和二阶非线性光学性质的理论研究

用INDO/2和INDO/SCI方法计算了C₆₀(C≡N)₂和C₆₀C(C≡N)₂基态电子结构和电子光谱,所得结果与实验值基本一致.在此基础上,用ZINDO-SOS方法计算了两个分子的二阶非线性光学系数β_ijk和β_μ,并对其结果进行了分析和讨论.结果表明,乙氰基与C₆₀相连的两种碳笼衍生物都有大的非线性光学系数,C₆₀C(C≡N)₂是有希望的非线性光学材料.     

N－甲基-吡咯烷并[3,4]C60衍生物的结构、电子光谱 和二阶非线性光学性质的 理论研究

利用半经验AM1量子化学方法研究了N－甲基－吡咯烷并[3,4]C60(MPC)及其噻吩取代衍生物(TMPC)的几何结构。电子结构研究表明,MPC及TMPC衍生物的前沿轨道主要由C60部分决定,C60母体与成基团之间存在较强的分子内电荷转移,C60部分是电子受体,而噻吩环部分和吡咯环部分为电子给体。在AM1优化几何构型的基础上,用INDO/SCI方法计算了MPC及TMPC的电子光谱,用完全态求和(SOS)公式计算了其二阶非线性光学性质。结果表明,MPC与TMPC在400nm以上均存在吸收峰,TMPC的这些吸收峰(400nm以上)比MPC的吸收峰强得多,与实验所得结果一致。对于TMPC来说,其二阶非线性光学系数β0值随分子构型不同而有较大的变化,β0值最大可达60×10^-30esu。     

石房蛤毒素(STX)衍生物的电子结构与毒性-结构关系研究

本文对十个石房蛤毒素(Saxitoxin,STX)衍生物进行了量子化学(INDO)计算,得到了多种电子结构信息。据此研究了它们的电子结构特征,确定了它们的活性部位。通过构效关系研究,发现某些电子结构指数与毒性之间存在较好的相关关系。这些结果为讨论该类化合物的作用机理、与受体之间的相互作用及进一步的分子设计提供了有价值的信息。     

关于二阶非线性光学性质的分子设计研究

在INDO/CI基础上,用完全态求和公式自编程序计算二阶非线性光学系数β_ijk,考察了分子骨架、受电子基团或给电子基团变化对β_x的影响,并设计了最大β_x的化合物、计算结果均与实验值相符。     

杜鹃花科植物有毒成分的电子结构及构效关系

本文应用INDO方法, 对由杜鹃花科植物中提取分离的九个化合物进行了量子化学计算, 得到了分子轨道波函数等多种电子结构信息, 并计算了这些化合物活性部位的分子静电势, 得到了静电势图。用分子图形技术与药理性质相同的其它生物碱类毒素进行了空间结构比较。研究了它们的电子结构特征和活性部位, 讨论了作用机理及电子结构与毒性之间的关系。     

Approaching bulk limit for three‐dimensional solids via the cyclic cluster approximation: Semiempirical INDO study

The cyclic cluster method has been examined for a number of solids using a recently developed computer code, Solid 98. Calculations are based on the quasirelativistic (QR) INDO/1 (intermediate neglect of differential overlap) method that is simple enough to allow for a saturation of the (cyclic) clusters. Convergence toward the bulk limit (INDO/1) charge density with respect to the size of the model cyclic cluster is shown for diamond, silicon, germanium, boron nitride, gallium phosphide, gallium arsenide, and gallium antimonide. Results show that, as soon as the initial cluster size reaches 5 to 6 nm, one can safely use the obtained density matrix as a good approximation to the bulk limit. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 253–261, 1999     

Electronic conductive and corrosion mechanisms of dual nanostructure CuCr-doped hydrogenated carbon films for SS316L bipolar plates

The carbon-coated metal bipolar plate is believed to be a potential substitute of the traditional graphite bipolar plate. However, instead of pyrolytic graphite, carbon films grown by using hydrocarbon as the carbon source have a higher deposition rate but lower conductivity. Aiming to resolve this complaint, here, a new strategy of in-situ catalytic decomposition of methane via reactive magnetron sputtering of a Cr_0.6Cu_0.4 target in methane and argon atmosphere was proposed without heating. A dual structure C_18.6Cr_0.06Cu (S65) film with graphene-like carbon bridged nano-Cu clusters within amorphous carbon clusters embedded, which has a deposition rate (~24.1 nm/min) about four times higher than other reports (≤6.2 nm/min), with the interface contact resistance of 7.34 mΩ cm². The distinct mechanisms of good conductive and anti-corrosion can be understood as (1) the bridged nano-Cu clusters and graphene-like carbon structures construct an interconnected network in the bulk S65 film, endowing the S65 good conductivity, (2) the nano-Cu clusters are isolated by the graphene-like carbon structures and amorphous carbon clusters, which protect the nano-Cu clusters un-contacting with the corrosive medium, bringing the S65 excellent anti-corrosion properties. Our work opens a new route for the rapid deposition of carbon film for bipolar plate application.     

Structural investigation of zeolite-templated, ordered microporous carbon by scanning tunneling microscopy and Raman spectroscopy

Scanning tunneling microscopy (STM) and Raman spectroscopy have been employed for a detailed structural characterization of an ordered microporous carbon synthesized in the nanochannels of zeolite Y by a templating approach. The carbon exhibited an exceptionally high adsorption capacity together with a long-range structural organization on the nanometer scale. As revealed by STM, this material exhibited both terrace-like and periodic (approximately 1.4 nm) stripe-like nanostructures. The vertical separation between contiguous terraces was measured to be also about 1.4 nm and was thus coincident with the structural periodicity deduced by X-ray diffraction. The terraces of the carbon material were shown to consist of arrays of approximately 1 nm wide carbon clusters. The carbon clusters displayed only a limited degree of local order within the terraces but not long-range periodicity. Likewise, STM indicated that the micropore structure of this carbon originated from the large number of voids that separate adjacent clusters, being morphologically very different from that commonly found in activated carbons. The range of void sizes measured by STM (0.8-2.3 nm) was in complete agreement with the pore size distribution determined from nitrogen adsorption measurements. The origin of the nanostructural features observed for this microporous carbon was discussed on the basis of the surface structure of the zeolite Y template. Finally, Raman spectroscopy provided evidence that the carbon clusters were made up of nanographenes with a curved topology.     

Molecular dynamics study of the catalyst particle size dependence on carbon nanotube growth

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, which contain at least 20 iron atoms, nucleate SWNTs that have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm.     

Water cluster growth in hydrophobic solid nanospaces

The growth mechanism of water clusters in carbon nanopores is clearly elucidated by in situ small-angle X-ray scattering (SAXS) studies and grand canonical Monte Carlo (GCMC) simulations at 293-313 K. Water molecules are isolated from each other in hydrophobic nanopores below relative pressures (P/P(0)) of 0.5. Water molecules associate with each other to form clusters of about 0.6 nm in size at P/P(0)=0.6, accompanied by a remarkable aggregation of these clusters. The complete filling of carbon nanopores finishes at about P/P(0)=0.8. The correlation length analysis of SAXS profiles leads to the proposal of a growth mechanism for these water clusters and the presence of the critical cluster size of 0.6 nm leads to extremely stable clusters of water molecules in hydrophobic nanopores. Once a cluster of the critical size is formed in hydrophobic nanopores, the predominant water adsorption begins to fill carbon nanopores.     

Carbon nanofiber supported palladium catalyst for liquid-phase reactions: An active and selective catalyst for hydrogenation of cinnamaldehyde into hydrocinnamaldehyde

Carbon nanofibers (CNFs) prepared by decomposition of ethane over a Ni/alumina catalyst, are used as support for palladium clusters. The carbon support displays a mean diameter of 40–50 nm, lengths up to several tens of micrometers, as highlighted by transmission electron microscopy (TEM) observations and a specific surface area of about 50 m²/g. The spheroidal palladium particles have a relatively homogeneous and sharp size distribution, centered at around 4 nm. This novel Pd/carbon nanofiber catalyst displays unusual catalytic properties and is successfully used in the selective hydrogenation of the C=C bond in cinnamaldehyde at a reaction temperature of around 80°C, under continuous hydrogen flowing at atmospheric pressure. The high performances of this novel catalyst in terms of efficiency and selectivity are, respectively, related to the inhibition of the mass-transfer processes over this non-porous material and to peculiar palladium–carbon interactions. It is concluded that the absence of microporosity in the carbon nanofibers favours both the high activity and selectivity which is confirmed by comparison with the commercially available high surface area charcoal supported palladium catalyst.     

Influence of the INDO parameterization on the indirect spin–spin coupling constants as calculated by the FPT INDO method

Alterations have been introduced in the semi-empirical INDO parameters in order to study their influence on the Fermi contact term of the indirect spin–spin coupling constants as calculated by the finite perturbation theory (FPT). For this purpose a set of molecules containing hydrogen, carbon and/or fluorine has been selected. In general, most coupling constants are found to be much more sensitive than other molecular properties to small changes in the INDO parameters. This sensitivity depends strongly on the particular calculated coupling constant. In most cases the uncertainty in the INDO parameters leads to uncertainties in the coupling constants which are much greater than their experimental errors.     

The structure and properties of a new type of nanostructured composite Si/C electrodes for lithium ion accumulators

The results obtained in studies of the structure and electrochemical properties of film electrodes prepared by magnetron plasma sputtering of silicon and graphite and working under the conditions of lithium injection and extraction are generalized. Composite silicon-carbon electrodes synthesized by depositing silicon and carbon nanolayers with the use of a magnetron plasma were films 100–500 nm thick. Part of them exhibited highly uniform nanogranular structure based on a carbon matrix with inserted silicon clusters of size below 6 nm. The nanogranular structure of Si/C composites was observed for the first time; such a morphology was not characteristic of not structured silicon layers deposited under equal conditions. The factors that determined the electrochemical charging-discharging behavior of new composites were the degree of uniformity of the nanogranular structure, the ratio between the silicon and carbon components, and film thickness. For two thin films, the initial composite capacitance was higher than that corresponding to the Li_4.4Si stoichiometry for the silicon component and LiC₆ stoichiometry for the carbon component, which was related to the special nanostructured state of silicon and carbon. The effects (luminescence band and absorption bands in the visible range) characteristic of nanosized silicon particles were observed.     

Crystal structures and electronic properties of BaC_2 isomers by theoretical study based on DFT

Band structures and electronic properties of two BaC2 isomers were calculated by using density func-tional theory(DFT) properly.The ionic bond features are all typical between cation(Ba) and anion clusters(C2) in both structures of the isomers.However,a much stronger covalent bond exists in anion clusters which can be seen by inspecting the electron distribution contour that has a dull bell like shape between two carbon atoms.The shortest distance between Ba2 and C22? and the bond length in anion clusters are different in these isomers of BaC2,which are 0.2945 nm and 0.1185 nm for the structure with the I4/mmm space group and 0.2744 and 0.1136 nm with the C2/c type,respectively.Band structures were clarified by combining the DOS to indicate the ionic bonding features more clearly.Population analysis provided further evidence on these ideas.Thermodynamical calculation results reveal that the transition temperature of these two polymorphs of BaC2 locates near 132 K,which is consistent with the recent experimental results.