自由基聚合中二硫酯结构及其活性的研究

用密度泛函方法,在B3LYP/6-31G+(d)水平上对三种二硫酯化合物进行了几何构型全优化.计算了C-S键离解能以及对于自由基的原子自旋密度,并且探讨了它们与化合物活性之间的关系,分析的结论与实验结论完全一致.同时结论也表明密度泛函理论计算能为C—S键离解能,原子自旋密度变化趋势提供一个很好的预测.     

Theoretical Study of the C-Cl Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds

利用密度泛函(DFT)三种交换/相关函数(B3LYP, B3PW91,B3P86)结合6-31G**和6-311G**基组,计算了13个取代氯苯化合物的键离解能. 结果表明B3P86/6-311G**方法是计算取代氯苯化合物键离解能的可信方法,研究发现C-Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C-Cl键的键离解能的影响不明显. 研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估.     

铝原子团簇Al5、Al5-和Al5+稳定结构的密度泛函理论研究

采用密度泛函理论的四种方法 :杂化密度泛函B3LYP与B3PW 91、Perdew Wang91交换与相关泛函WP91PW91、局域自旋密度近似SVWN ,研究了Al5、Al5-和Al5+ 团簇的多种可能结构 ,找到了它们稳定的结构与自旋态 ,与已有的理论结果作了比较 ,并计算了Al5-的绝热与垂直电子离解能、Al5的绝热与垂直电离势 ,同有关的实验数据比较 ,符合较好 .同时对四种密度泛函方法的计算结果作了一些比较与讨论     

C-F键核自旋偶合常数的理论研究

利用密度泛函中B3LYP方法,选择6-31G**3基组, 研究了四组分别为10、20、30、40个分子的C-F键的核自旋偶合常数,由此拟合出4个计算核自旋偶合常数的公式,并用4种化合物分别进行检验,理论计算值较好地与文献值相符合.     

黑索金的电子结构和热解机理的从头算研究

利用从头算梯度修正密度泛函理论,我们在B3LYP/6-31G(d,p)水平上,计算了高能炸药黑索金(RDX)及其热解中间产物C3H6N5O4和NO2等的电子结构、能量、键级和一些热力学性质,并在此基础上,计算了键离解能和反应速率常数.此外,我们还分别从键级和键离解能角度,讨论了RDX的热解机理,所得结果与实验一致.     

环状氮氢化合物NnHn(n=3~5)的构象研究

应用密度泛函理论对10种环状氮氢化合物异构体进行了研究。利用自然键轨道理论(NBO)和分子中的原子理论(AIM)分析了这些异构体的成键特征、相对稳定性。N-N键长与键临界点的电荷密度存在反比关系。超共轭作用和立体排斥作用计算表明:立体排斥作用和超共轭作用在决定构象稳定性的方面均起了主要的作用。H原子的相对位置的差异影响了键-键立体排斥能的类型。     

环状氮氢化合物NnHn(n=3~5)的构象研究

应用密度泛函理论对10种环状氮氢化合物异构体进行了研究.利用自然键轨道理论(NBO)和分子中的原子理论(AIM)分析了这些异构体的成键特征、相对稳定性.N-N键长与键临界点的电荷密度存在反比关系.超共轭作用和立体排斥作用计算表明:立体排斥作用和超共轭作用在决定构象稳定性的方面均起了主要的作用.H原子的相对位置的差异影响了键-键立体排斥能的类型.     

Ni4PrB的电子结构和磁性能研究

考虑Pr-4f及Ni-3d电子间的库仑作用U和交换作用J,采用局域自旋密度近似LSDA(Local spin-density approximation)及LSDA+U(在位库仑势)近似,对Ni₄PrB化合物进行结构优化,并计算体系电子结构,能带结构和磁性能. 结果显示,Ni₄PrB具备金属半导体性质,存在Pr-Ni铁磁耦合. U的引入对体系磁特性和结构稳定性有关键作用,加U前体系磁性来源为Ni原子磁矩,加U后体系磁性来源为Pr原子,且体系稳定性提高,U值的作用对于修正体系强关联有重要影响,可以合理描述由强关联和自旋排斥引发的排斥效应. 关键词： 密度泛函理论 电子键结构 磁性能 稀土过渡金属间化合物     

含alphaC-H键的硝基芳香族炸药分子的C-NO2键离解能研究

采用密度泛函理论中的B3LYP方法,取6-31G*基组,对含alpha C-H键的硝基苯类炸药的分子结构和能量,以及C-NO2键离解能等进行计算,讨论了含alpha C-H键的硝基苯类炸药分子中C-NO2键离解能的强弱与其位置的关系。研究表明:alpha C-H键邻位的C-NO2键离解能比对位的C-NO2键离解能弱,邻位中又以受alpha C-H键影响最大的C-NO2键离解能最弱。     

八极矩外电场作用下CH3的基态和激发态研究

采用密度泛函和含时密度泛函方法在6- 311g**基组水平上对比研究了八极矩外电场对CH3自由基的几何构型、轨道能级分布、激发能、振子强度以及电偶极矩、原子电荷数和离解能等特性的影响.结果表明,在外电场作用下甲基的激发能,偶极矩和极化率上升,离解能下降,说明较强外电场的作用有助于CH3的离解.     

Coexistence of Magnetism and Conductivity in Bis(ethylenediseleno) Tetrathiafulvalene (BEST) with Octahedral Anions Hexacyanoferrate (III)and Nitroprusside

Using an accurate density-function method, we explore the coexistence of the magnetism and conductivity in bis(ethylenediselena)-tetrathiafulvalene (BEST) with the paramagnetic hexacyanoferrate(III) [Fe(CN)₆]^3- or the photochromic nitroprusside anion [Fe(CN)₅NO]^2-. The total and partial densities of states, and the atomic spin magnetic moments are calculated and discussed. It is found that the up- and down-spin total densities of states (DOS) are continuous in the vicinity of the Fermi level, there is overlap between the HOMO and LUMO in the up-spin subbands and the down-spin subbands, which reveals that these types of compounds have conductive properties. From the total and partial densities of states and atomic spin magnetic moments, it is shown that the spin magnetic moments of (BEST)₄[Fe(CN)₆] is mainly assembled at the iron atom and the cyanogen radical, and the spontaneous magnetic moments for (BEST)₂[Fe(CN)₅NO] come from iron atom, cyanogen and nitric oxide radical. To our best knowledge, it is the first theoretical study on the coexistence of the magnetism and conductivity of these compounds.     

On the centrifugal distortion in the microwave spectra of O2 and SO

Stable radicals formed by room temperature X-irradiation of single crystals of acridine and phenazine have been identified and their structures determined by detailed ENDOR studies at 77 K. The E.S.R. spectra are of little assistance in the identification of these radicals. However, the high resolution of ENDOR has made it possible to study all the proton hyperfine interactions in detail. The radicals investigated in this study are formed as a result of the addition of atomic hydrogen to the nitrogen atom of the acridine and phenazine molecules. ENDOR lines of all the protons have been identified and analysed. Spin densities have been deduced from the proton hyperfine tensors. Although the unpaired electron is extensively delocalized throughout the molecule, there are large spin densities (0·475 and 0·584, respectively) on C₉ in acridine and the second nitrogen in phenazine. Excellent agreement has been obtained between the observed spin densities and those computed by INDO molecular orbital calculations. The design and construction of a simple rectangular ENDOR cavity operating in the TE₁₀₁ mode is described.     

The electronic structure and the ferromagnetic intermolecular interactions in the crystal of TEMPO radicals

Based on the generalized gradient approximation, full potential linearized augmented plane wave (FP-LAPW) calculations have been performed to study the electronic band structure and the intermolecular ferromagnetic (FM) interactions for the two TEMPO radicals 4-Benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (1) and 4-(2-naphtylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl (2). The total and the partial density of states and the atomic spin magnetic moments are calculated and discussed. The calculation revealed that the two TEMPO radicals have the intermolecular FM interactions, and the spontaneous magnetic moment is 1.0 μ_B per molecule of each crystal, which is in good agreement with the experimental value. It is found that the unpaired electrons in these compounds are localized in a molecular orbital constituted primarily of π* (NO) orbital, and the main contribution of the spin magnetic moment comes from the NO-free radical. The origin of FM is also studied in detail.     

二苯二硫和二苄二硫润滑性能的量子化学研究

用Gaussian03W程序在B3LYP/631G和HF/631G水平上对二苯二硫(DPDS)和二苄二硫(DBDS)的分子几何构型、电子结构、分子轨道指数及与铁原子簇的相互作用等进行了理论计算.用前线分子轨道理论分析了反应的活性原子和活性键,讨论了DPDS和DBDS与铁原子的作用方式,用前线电子密度,超离域性指数,原子净电荷及化合物与铁原子簇的化学吸附作用能等参数作为判据分析了DPDS和DBDS与铁原子间键合的强弱,反应性的大小.计算结果表明DPDS和DBDS与铁接触时,趋向于S-S键与C-S键断裂,在较为缓和的摩擦条件下,DPDS的抗磨作用优于DBDS,在较为苛刻的摩擦条件下,DBDS的极压作用优于DPDS,与摩擦学试验结果一致.     

Magnetic and electronic properties of NiAs-type chromium chalcogenides

We have computed spin-dependent energy bands, spin moments and density of states of NiAs-type CrX (X=S, Se and Te) chalcogenides using linear combination of atomic orbitals method within density functional theory as well as full potential augmented plane wave method. In addition, magnetic properties have also been computed using spin polarized relativistic Korringa-Kohn-Rostoker method. We have also obtained the first ever theoretical electron momentum densities of CrX compounds considering linear combination of atomic orbitals and compared the results with the isotropic Compton profiles measured using 20 Ci ¹³⁷Cs Compton spectrometer. The Fermi surface topology and magnetic properties are discussed in terms of majority and minority energy bands and density of states. In addition, to highlight the role of Cr (3d) electrons in such type of chalcogenides, we have also reported the magnetic Compton profile of CrTe using the Korringa-Kohn-Rostoker method.     

Electron spin resonance of phosphorescent fluorine-substituted aromatics

The lowest excited triplet state of the three compounds naphthalene, 1-fluoronaphthalene and 2-fluoronaphthalene, has been investigated by electron spin resonance spectroscopy. The phosphorescent molecules were oriented and diluted in durene single crystals. Zero field energies, principal values of the g tensors and hyperfine coupling constants for hydrogen and fluorine nuclei in the three canonical orientations are reported. A detailed comparative analysis of these results shows that the presence of fluorine has little effect on the π-electron distribution in the excited state. Upon substitution, some of the spin density originally present in the carbon 2pπ orbital spreads onto the fluorine atom. Spin densities on other carbon atoms remain constant. This local perturbation model is used to analyse in detail the magnetic properties of phosphorescent 1- and 2-fluoronaphthalene. From the spin densities and the experimental coupling constants, the hyperfine tensor of a C-F fragment bearing unit spin density is derived. This tensor is then broken down into four contributions which are computed using a minimum number of assumptions. The results are: (i) accurate experimental data pertaining to the nature of the C-F bond and its spin delocalization and polarization mechanisms; (ii) a firmly-established hyperfine tensor for fluorine in a planar, sp ² hybridized fragment. A simple method to determine spin densities using fluorine hyperfine structure as a probe is outlined.     

Gaussian polynomial method for spin-dependent level density and new formula for spin distribution

Large-scale combinatorial calculations of level densities were performed for selected nuclei using Gaussian polynomial generating function method (GPM). Contrary to the results of previous combinatorial calculations, we find a good agreement of the combinatorial total level densities and Bethe formula. Combinatorial GPM calculations were performed also for spin-dependent level densities and comparison is made with various algebraic formulas. On the basis of our GPM calculations we propose a new phenomenological spin-dependent level density formula, which in the low-spin limit reduces to the spin-dependent formula of Bethe. The new formula (24) is for all spins factorized into the product of total level density and spin distribution function, where the spin distribution function (25) contains an additional spin correction parameter.     

Effects of resveratrol and its analogs on scavenging hydroxyl radicals: Evaluation by EPR spin trapping method

Resveratrol (3,4′,5-trihydroxy-trans-stilbene) and six analogs, polyhydroxystilbenes, were synthesized. Their effects on scavenging hydroxyl radicals were studied by electron paramagnetic resonance (EPR) spin trapping method. The EPR signal intensity of the spin adduct of hydroxyl radical to 5,5-dimethyl-1-pyrroline N-oxide was detected and used as a standard for the evaluation of the effect of the seven compounds on scavenging hydroxyl radicals. While all seven compounds exhibited hydroxyl radical-scavenging activity, some of them proved to be more effective than resveratrol in this model. Another stable but low-intensity spin adduct was also observed by EPR. A possible assignment is proposed.