富勒烯衍生物C50X(X=SiH2,PH,S)的结构及稳定性的理论研究

用从头算HF/3-21G方法研究了C50的环加成衍生物C50X(X=SiH2, PH, S)所有可能的异构体的结构与稳定性, 计算结果表明, SiH2基团、PH基团与S原子在C50上环加成的优先加成位置相同, 都为C3—C4类键和C4—C4类键, 并且相应形成[5,6]-闭环和[5,5]-闭环结构的最稳定异构体; 决定C50X(X=SiH2, PH, S)各异构体稳定性的主要因素, 因加成位置以及发生加成反应的C—C键的单双键类型的不同, 可能是张力、共轭效应或者二者的共同作用. 进一步比较了C50X(X=SiH2, PH, S)与C50X(X=CH2, NH, O)的结构和稳定性等, 并总结出规律性的结论, 即加成原子的大小和加成位置C—C键的类型是影响形成开环或闭环结构的C50环加成衍生物的两种主要因素.     

Hydrogen abstraction of methanimine by X12N12 (X = B,Al) nanoclusters: a DFT study

Structural Chemistry - In this work, dissociative adsorption of methanimine (CH2NH) on the surface of B12N12 and Al12N12 nanoclusters is studied at wB97XD/6-31G(d) computational level. The results...     

Structure and Stability of Endohedral Complexes X @（HAlNH）12 （X = He, Ne, Ar, Kr）

1 INTRODUCTION The structure and property of endohedral com- plexes X@An have been well represented, including Fullerene structures with bigger volume, such as Ln3 @C60[1], Sc3N@C80[2] and Sc3N@C78[3], or metal cluster complexes of Al(Al13-)[4] and Ga(Ga13-)[5] with relatively smaller volume. These studies have revealed much structure and property information, for example, the impact of building-in atom X on the cage structure, the interaction character of X-An in the cage, and the…     

(XY)12(X=B,Al;Y=P)团簇的结构与稳定性

采用B3LYP／6031G*方法,对(XY)12(X=B,Al;Y=P)笼状团簇的同分异构体进行优化,筛选出能量最低的构型．讨论它们的几何构型、HOMO-LUMO能隙、生成焓、核独立化学位移(NICS)和自由能．得到(BP)12和(AlP)12团簇的最稳定构型均为具有Th对称性的四、六元环组成的笼,亚稳态结构中含有五元环。     

Influence of Ti, V, and Ni Dopants on the Electronic Structure and Chemical Bonding in Cubic Silicon Carbide

The electronic structure and chemical bond parameters were studied for 3C–SiC systems with Ti, V, and Ni dopants by the ab initio discrete variation method. Possible dopant (M) sites in crystal are taken into account. As dopant sites we consider the interstitial (M_i) and substitution (M_s) positions. Pair type defects are modeled: M_i–Si vacancy and M_s–Si_i defect.     

内含式复合物X@(HAlNH)12 (X=Be,Mg, Ca,Zn, Al+, Ga+)的结构和稳定性

在研究闭式多面体(HAlNH)12簇合物几何构型及稳定性的基础上, 用DFT的B3LYP方法在6-31G(d)的水平上, 对其内含式复合物X@(HAlNH)12 (X= Be, Mg, Ca, Zn, Al+, Ga+)进行了构型优化和能量计算, 并讨论了稳定结构的几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系. 用Gaussian 03的QST3方法确定了客体X通过笼面6-元环的迁移过渡态(TS)结构, 并用IRC方法对所得TS结构进行了验证. 最后得到内含式复合物X@(HAlNH)12结构在热力学和动力学上的稳定性信息, 其中复合物Ga+@(HAlNH)12的结构相对最稳定.     

C_(56)X_(10)(X=F,Cl,Br,I)的结构稳定性和电子性质

采用密度泛函理论(DFT)中的广义梯度近似(GGA)方法对C56X10(X=F,Cl,Br,I)的结构稳定性和电子性质进行了计算研究.结构稳定性计算表明:对于C56X10(X=F,Cl,Br,I),能隙、反应热、最大振动频率和最小振动频率都随着X原子序数的增加而减小,表明C56X10(X=F,Cl,Br,I)的稳定性随着X原子序数的增加而逐渐降低,其中C56F10最为稳定.前人在实验上已成功合成出C56Cl10,因此,我们推测C56F10有望在实验上成功合成.前线轨道计算发现,C56相邻的五边形公共顶点以及两个六边形-五边形-六边形公共顶点是笼子中化学活性最强的部位,有利于卤族元素的外部吸附.此外,计算结果还显示,C56X10(X=F,Cl,Br,I)的电负性随着X原子序数的增大而逐渐减弱,C—X基团的电负性因位置的不同而不同.     

X@(HAlNH)12和X(HAlNH)12 (X＝F－, Cl－, Br－, O2－, S2－, Se2－)复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上, 对闭式多面体簇合物(HAlNH)₁₂及其内含式X@(HAlNH)₁₂和外接式X(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, O^2－, S^2－, Se^2－)复合物的结构进行了构型优化和能量计算, 并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系, 最后得到复合物结构的稳定性信息, 具有T_h对称性的X@(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, S^2－, Se^2－)复合物和具有C₃对称性的O^2－@(HAlNH)₁₂复合物为内含式的基态结构, 从能量角度分析, 内含式复合物比外接式复合物的结构稳定.     

Electronic Structure of Fe+X Alloys (X = Si, Ge, Co)

The electronic structure of Fe–Ge, Fe–Si, and Fe–Co alloys has been investigated by X-ray photoelectron spectroscopy. In Fe–Ge alloys with less than 10 at.% Ge, the Fe–Ge bond is mainly formed by the Fe 4sp- and Ge 4p-electrons. The results obtained for this system are identical to those for the Fe–Si system. The form of the valence band reflects the density distribution of both iron d-electronic states the and p-electronic states of the second component, having more extended density distribution of valence electrons. In FeCo alloys, strong spatial localization of d-electron density takes place in the vicinity of the corresponding atoms, which is stronger on the iron atoms compared to pure iron; the valence band has a two-band structure reflecting the density distribution of the d-states of each component. X-ray photoelectron spectroscopy data are in good agreement with kinetic data for the alloys.     

Computational study of the reactions of SiH3X (X=H, Cl, Br, I) with HCN

Ab initio calculations were carried out for the reactions of silane and halosilanes (SiH3X, X=H, Cl, Br, I) with HCN. Geometries of the reactants, transition states, intermediates and products were optimized at HF, MP2, and B3LYP levels of theory using the 6-31G(d) and 6-31G(d,p) basis sets. Energies were also obtained using G3MP2 and G3B3 levels of theory. Intrinsic reaction coordinate (IRC) calculations were performed to characterize the transition states on the potential energy surface. It was found that HCN can react with silane and halosilanes via three different mechanisms. One involves HX elimination by a one-step pathway producing SiH3CN. The second mechanism consists of H2 elimination, producing SiH2XCN via a one-step pathway or three multiple-step pathways. The third mechanism involves dissociation of SiH3X to various products, which can then react with HCN. Activation energies, enthalpies, and free energies of activation along with the thermodynamic properties (DeltaE, DeltaH, and DeltaG) of each reaction pathway were calculated. The reaction of SiH3X with HCN produce different products depending on substituent X. We have found that the standard 6-31G(d) bromine basis set gave results which were in better agreement with the G3MP2 results than for the Binning-Curtiss basis set. Computed heats of formation (DeltaHf) for SiH3CN, SiH3NC, SiH2ClCN, SiH2BrCN, SiH2ICN, SiHCl, SiHBr, and SiHI were found to be 133.5, 150.8, -34.4, 23.6, 102.4, 48.7, 127.1, and 179.8 kJ mol-1, respectively. From enthalpies calculated at G3MP2, we predict that the DeltaHf for SiH2 to be 262.8 kJ mol-1 compared to the experimental value of 273.8+/-4.2 kJ mol-1.     

ChemInform Abstract: Comparative Studies on the Phase Stability,Electronic Structure,and Topology of the Charge Density in the Li3XO4 (X: P,As, V) Lithium Orthosalt Polymorphs

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Ab initio Calculations of the Geometry,Electronic Structure,and Vibrational Spectrum of (Acetoxymethyl)triflouorosilane

The geometries and electronic structures of various conformers of (acetoxymetyl)trifluorosilane, CH₃C(O)OCH₂SiF₃, and also the frequencies and intensities of its vibration bands were studied by ab initio [RHF(6-31G*)] calculations. According to the experimental spectra and calculation results, the most stable is the conformation in which the donor-acceptor interaction = OSi is realized. Analysis of the geometry, atomic charges, and molecular orbital energies shows that this donor-acceptor bond is mainly due to interaction of the lone electron pairs of the carbonyl oxygen atom with the vacant * orbitals of the C-Si-F _a moiety.     

单壁AlAs(111)纳米管结构和电子性质的密度泛函理论研究

通过卷曲立方AlAs(111)单层片(sheets)构造了一系列(n,0)和(n,m)一维单壁纳米管。用周期性密度泛函理论(DFT)计算并比较了不同类型AlAs纳米管在几何结构、能量及电子性质等方面的差别。计算结果表明锯齿型和椅型纳米管应变能均为负值,并随着管径变大而逐渐变小。然而,它们的带隙相当不同:椅型纳米管为间接带隙,随着管径的增大而带隙减小;锯齿型纳米管为直接带隙,管径为1.87 nm时存在着一个极大带隙值(2.11 eV)。这种不同主要源于锯齿型纳米管铝原子间3p轨道的耦合贡献。     

Exploring Electronic Properties of Si20-n H20-n P n Heterofullerenes (N = 1, 2, 5, and 10) Based on NMR and NBO Analysis: A DFT Study

Abstract

Density functional theory (DFT) calculations are performed to characterize Si_20-nH_20-nP_nheterofullerenes (n = 1, 2, 5, and 10), and to examine the stability of encapsulated X@Si_20-nH_20-nP_nwhere X = Li, Na, and K. To this aim, ²⁹Si, ³¹P, and ¹H chemical shielding (CS) tensors as well as natural charges are calculated for the optimized structures. The local structures around silicon as well as phosphorus nuclei are found to show a good correlation with CSs. However, the similar values of ¹H calculated CSs (26–28 ppm) obtained for all the heterofullerenes mean hydrogen atoms do not detect the local structure around the adjacent silicon and also do not distinguish between isomers of heterofullerenes and the number of P dopants. According to calculated endo-hedral inclusion energies (E_inc), formation of the Li@Si_20-nH_20-nP_ncomplexes, unlike the K@Si_20-nH_20-nP_nones, are exothermic while E_incof the Na@Si_20-nH_20-nP_ncomplexes strongly depends on the position and number of P dopants. Moreover, binding energies for the considered models are found to be in the order of Si_20-nH_20-nP_n> Li@Si_20-nH_20-nP_n> Na@Si_20-nH_20-nP_n> K@Si_20-nH_20-nP_nwhile strongly depending on the pattern of P dopants on the surface of the cage.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the following free supplemental files: Additional figures and tables]     

(XY)12 (X═B, Al; Y═P)团簇的结构与稳定性

采用B3LYP/6-31G*方法, 对(XY)₁₂ (X═B, Al; Y═P)笼状团簇的同分异构体进行优化, 筛选出能量最低的构型. 讨论它们的几何构型、HOMO-LUMO能隙、生成焓、核独立化学位移(NICS)和自由能. 得到(BP)₁₂和(AlP)₁₂团簇的最稳定构型均为具有T_h对称性的四、六元环组成的笼, 亚稳态结构中含有五元环.     

X@(HAINH)_(12)和X(HAINH)_(12)(X=F~-,Cl~-,Br~-,O~(2-),S~(2-),Se~(2-))复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上,对闭式多面体簇合物(HA1NH)12及其内含式X@(HA1NH)12外接式X(HA1NH)12(X=F-,Cl-,Br-,O2-,S2-,Se2-)复合物的结构进行了构型优化和能量计算,并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系,最后得到复合物结构的稳定性信息,具有Th对称性的X@(HA1NH)12(X=F-,Cl-,Br-,S2-,Se2-)复合物和具有C3对称性的O2-@(HA1NH)12复合物为内含式的基态结构,从能量角度分析,内含式复合物比外接式复合物的结构稳定.