Arrhenius活化能理论的修正

针对Arrhenius活化能理论的不足,修正了这个理论,建立了一个修正的Arrhenius方程,它能适用于更宽的温度范围。     

溯源辨析国内大学化学教材关于碰撞理论中活化能的定义

目前国内化学基础课教材关于碰撞理论中活化能的定义存在严重分歧,简单总结了目前中文教材中的3种定义。通过对碰撞理论形成过程中部分历史背景的梳理,总结出碰撞理论所具备的2个基本要素即气体分子运动论的应用以及碰撞活化假设,然后溯源3种不同定义来源的历史文献,从2个基本要素的角度分析3种定义。研究发现中文教材广泛采用的Lewis活化能解说不承认碰撞活化假设,采用了辐射活化假说,同时表述笼统不严谨,Tolman活化能解说是单纯的统计力学处理,没有应用气体分子运动论,不属于碰撞理论范畴。而简单碰撞理论提出的有效碰撞的最低能量作为活化能的定义更能承载碰撞理论的基本要素。     

共聚物铑配合物催化甲醇羰基化速控步骤的理论研究

采用以原子重叠及电子离域的分子轨道理论ＡＳＥＤ ＭＯ（含原子对排斥的ＥＨＭＯ法）为基础的结构自动优化法，对共聚物铑配合物催化甲醇羰基化制乙酸反应速率控制步骤 氧化加成进行了理论研究．计算了不同共聚物配体形成的铑催化剂与碘甲烷的氧化加成反应途径，并得到反应活化能，分析了氧化加成反应过程中的电子转移和空间因素对活化能的影响，计算结果与实验结果是相符的，并从理论上解释了２ 乙烯基吡啶形成的共聚物铑配合物催化活性高于４ 乙烯基吡啶形成的共聚物铑配合物催化活性的原因．     

AlCl歧化反应分解法制备金属铝过程中[AlCl]_n的形成机理

利用密度泛函理论(DFT)中的广义梯度近似(GGA)法,对氧化铝真空还原氯化歧化法制备金属铝的过程中[AlCl]n(n=1-10)团簇的稳定结构、能量和团簇形成过程的过渡态及其振动频率进行了理论研究,预测了其基态结构及成长趋势.结果表明:[AlCl]n(n=1-10)团簇可能存在的结构都是以[Al]n骨架外接n个Cl原子成型,且具有较好的几何对称性;从过渡态计算得到的活化能来看,正过程的活化能总是比逆过程的活化能要小,即[AlCl]n(n=1-10)团簇具有较好的成长趋势.以上研究结果有助于进一步了解用碳热还原氯化歧化法制备金属铝过程中液态金属铝的生成.     

BrSSCl和SSBrCl相对稳定性的理论研究

采用量子化学中的密度泛函理论，在B3LYP／6-311 G(3df)水平上全优化得到了S2BrCl分子线型和分叉型2种异构体的平衡结构，同时对可能发生的分子内原子迁移过程的过渡态进行了考察。计算结果表明，从能量角度看，线型的BrSSCl为稳定构型。采用统计热力学及过渡态理论，研究了Z种平衡结构之间相互转化的热力学和动力学性质。根据计算结果，无论是Cl迁移还是Br迁移，分子内的原子迁移都需要较高的活化能，并且迁移速度较慢。     

S2ClF的构型及其异构化反应的密度泛函理论研究

采用量子化学中的密度泛函理论B3LYP方法,在6-311+G(3df)水平上,全优化得到了S2ClF线型和分叉型2种异构体的平衡结构,同时对可能发生的分子内卤素原子迁移反应的过渡态进行了考察。计算结果表明,从能量角度看,线型的ClSSF为稳定构型,热力学和动力学计算表明,无论是F原子迁移还是Cl原子迁移,分子内的原子迁移需要较高的活化能,并且速度很慢。     

高中教学中如何讲授化学反应的活化能

对比了人教版、苏教版以及鲁科版对化学反应活化能的有关论述。介绍了IUPAC（1996）推荐的活化能的定义,强调了为什么仅有基元反应活化能才有准确的解释（即Tolman的统计观点）,最后提出了在高中阶段如何讲授化学反应活化能的几点建议。     

2-巯基吡啶质子迁移过程的理论研究

采用密度泛函理论,在B3LYP/6-311G**基组水平上,计算并考察了2-巯基吡啶分子硫醇式结构和硫酮式结构进行结构互变质子迁移过程中的4种可能途径:(a)分子内质子迁移,(b)水助质子迁移,(c)同种二聚体双质子迁移和(d)异种二聚体间双质子迁移.计算结果表明,途经c所需要的活化能最小(9.73 kJ.mol-1,逆反应则为55.28 kJ.mol-1),而过程a所需要的活化能最大(106.02 kJ.mol-1),途径b和d的活化能居中间(分别为32.05和15.91 kJ.mol-1).研究还表明,氢键在降低反应活化能方面起着重要的作用.     

Fe3O4(111)面上的水煤气变换反应机理

水煤气变换是一重要的制备氢气的反应, 采用密度泛函理论(DFT), 对水煤气变换反应在Fe₃O₄ (111)面上的催化反应作了深入研究. 结果表明: 氧化还原机理的活化能明显高于结合机理的活化能, 中间步骤应以结合机理进行|氢原子结合生成氢气为整个反应的速控步骤, 理论计算其活化能与水煤气变换实验数据一致, 高达1.29 eV, 还对迄今有关水煤气变换机理研究中的各种实验现象作了合理的解释, 并对Fe₃O₄ (111)催化剂的改性设计作了讨论.     

分子在ITQ-3分子筛窄孔道内扩散的过渡态理论模型

建立了一个基于过渡态理论的分子在ITQ-3窄孔道方向扩散的模型. 该模型中, 由于分子从空腔中的一个吸附位越过势垒到相邻的另一个空腔中的吸附位需要克服很大的势垒能, 因而分子在势垒处可以简化处理为只存在排斥势, 可得到扩散系数依赖温度和Lennard-Jones作用参数的解析关系. 用分子动力学方法对CF₄在ITQ-3上扩散进行了模拟并验证了解析关系的合理性. 分子动力学模拟计算得到的扩散活化能、势垒能和吸附位势能与实际值相吻合. 模拟结果也显示了扩散系数依赖于附载量, 表现为先增大后减小的变化模式. 扩散活化能的计算证实了这一变化机理, 即当附载量增加时, 由于处于空腔中的分子彼此抬高了势能, 降低了扩散活化能, 使得扩散系数随附载量的增加而增大, 之后由于堵塞效应, 扩散系数随附载量的增加而逐步减小.     

Failures of the topological resonance energy method

The topological resonance energy (TRE) is nowadays considered as one of the most reliable indices of stability and aromaticity of conjugated molecules. Seven groups of examples are constructed showing that the TRE concept leads sometimes to obviously false chemical conclusions.Presented on the International Symposium on Aromaticity, Dubrovnik, Yugoslavia, September 1979.     

Some formal properties of ensemble density functionals

Formal properties of ensemble density functionals are examined. Expressions for the difference between energy functionals where the particle number differs by one are constructed in terms of their first functional derivatives for the universal energy functional, the electron–electron repulsion energy functional, and the interacting kinetic energy functional. Equations that must be satisfied by second and higher order functional derivatives are derived. It is also shown that the shape of ${\delta V_{ee}[\rho]\over\delta\rho({\bf r})}$ and ${\delta K[\rho]\over\delta\rho({\bf r})}$ , the functional derivatives of the mutual electron–electron repulsion, and kinetic energy, respectively, are separately particle number independent for particle numbers between successive integers. © 2013 Wiley Periodicals, Inc.     

Ab initio Calculation of Intermolecular Dispersion Energy and Induction Energy of Nitramide Dimer

The dispersion energies, induction energies and their exchange counterparts (exchange-dispersion and exchange-induction energies) between two interacting nitramide molecules at several separations are derived based upon symmetry-adapted perturbation theory (SAPT). The results show that (1) the effect of intramonomer electron correlation on dispersion energies and induction energies for nitramide dimer system is remarkable especially in the region near the van der Waals minimum distance (0.42 nm). (2) At smaller separations the dispersion energies and the induction energies are largely quenched by their exchange counterparts, and this case in induction interaction is much more remarkable than in dispersion interaction. (3) Since at shorter distances there exists the strong short-range interaction due to electron transfer which quickly decays and even disappears at larger separations, the two different R-dependency formulae of induction energies were found: one is ca. R^-12.7 at short distances, and the other ca. R^-7.0 at large separations. The latter R-dependency is similar to that (ca.R^-7.2) of dispersion. (4) In the case of strong polar interaction existing in nitramide dimer, the “true“ induction correlation terms of higher order than ^1Eind^(22) may be important.     

Conformal Mixtures with Concentration-dependent Interactions; Application to Liquid Li—Mg

Abstract

The conformal model for binary liquids is extended to the case when the interaction energies are linear in the concentration, c. It is found that a suitably defined c-dependent ordering energy w is the single most important indication of the general character of the alloy, in particular of the behaviour of the excess free energy ΔF^XS and of the concentration fluctuation function S_cc . There are three cases:

• w is of fixed sign and varies by less than a factor of 2. Then ΔF^XS and S_cc —c(1 - c) both have opposite sign from w. The latter functions are largest (absolutely) in roughly the same region of c.

  w changes sign. Then ΔF^XS and S_cc —c(1 - c) are of opposite sign from w at each end of the diagram (much as one would expect on the basis of I).
  w is of fixed sign but varies by more than a factor of 2. Then ΔF^XS is of opposite sign from w and S_cc —c(1 - c) is mainly so. The latter function is, however, (marginally) of the same sign as w in a limited range of c at the end where w (and ΔF^XS ) is absolutely smallest. The alloy system Li-Mg appears to be of this type.

     

Calculation of correlation energy by many-body diagrammatic perturbation theory

The many-body diagrammatic perturbation theory is used for calculation of the correlation energy of closed-shell molecular systems. We apply Brueckner's concept of the two-particle renormalized interaction defined by a non-linear diagrammatic expression containing all possible (diagonal and/or non-diagonal) particle-particle, hole-hole and particle-hole intermediate elementary processes. Then, a “second-order” simple diagrammatic expression for the correlation energy can be formed, where the correlation energy is approximated by all the diagrams with biexcited intermediate states. An illustrative numerical application for the LiH molecule is presented. This article is dedicated to the memory of our friends and colleagues Dr. Jarka Surá and Dr. Marta Černayová, who tragically died in July 1976.     

DFT Investigations About Pyrazine Molecules on Si(100)-2×1 Surface

It is important to understand the interface of aromatic molecules on semiconductor surfaces because of the rich functionality of such molecules on semiconductor surfaces.The chemisorption of pyrazine molecules on the Si(100)-2×1 surface has been investigated using the B3LYP density functional theory with Si9H12 one-dimer and Si15H16 two-dimer cluster models.The calculated results predict that N-dative bonded-state,C2-C5 [4 2] and the tight-bridge1,2,5,6 products may coexist on the Si(100)-2×1 surface.     

DFT Investigations About Pyrazine Molecules on Si（100）-2×1 Surface

It is important to understand the interface of aromatic molecules on semiconductor surfaces because of the rich functionality of such molecules on semiconductor surfaces. The chemisorption of pyrazine molecules on the Si （100）- 2×1 surface has been investigated using the B3LYP density functional theory with Si9H12 one-dimer and Si15Hl6 two-dimer cluster models. The calculated results predict that N-dative bonded-state, C2=C5 [E4＋2] and the tight- bridgel,2,5,6 products may coexist on the Si（100）-2 × 1 surface.[第一段]     

聚丁二烯形变中内能贡献的预报

理想弹性体的统计理论假设弹性力完全由形变的构象熵所贡献的, 忽略了能量的贡献. 对于真实橡胶来说, 统计理论反映了它的主要特征, 然而真实橡胶与理想模型还是有差别的, 在拉伸过程中弹性力的贡献不完全是由熵所贡献的, 内能也会对弹性力有贡献, 并且, 不同的材料内能对弹性力的贡献(fe/f)不同[1], 这已为大量的实验事实所证实.     

Bonding in benzene methylene isomers: Modern VB study using spin-coupled theory

The electronic structure of the benzene methylene isomers fulvene, dimethylenecyclobutene, and trimethylenecyclopropene is studied using spin-coupled theory. It is shown that the three isomers all possess three noninteracting π-bonds and very low resonance energies. This is to be contrasted with benzene, where the symmetric coupling of the π-electron spins around the ring provides a considerable larger resonance energy. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 319–327, 1999     

DFT Investigations About Pyrazine Molecules on Si(100)-2×1 Surface

It is important to understand the interface of aromatic molecules on semiconductor surfaces because of the rich functionality of such molecules on semiconductor surfaces. The chemisorption of pyrazine molecules on the Si( 100)-2×1 surface has been investigated using the B3LYP density functional theory with Si9H12 one-dimer and Si15H16 twodimer cluster models. The calculated results predict that N-dative bonded-state, C2= C5 [ 4 2 ] and the tightbridge1, 2, 5,6 products may coexist on the Si(100)-2×1 surface.