碳溴键均裂离解能的理论研究

运用B3LYP,B3P86,BMK,M06和M06-2X这5种密度泛函理论方法分别对9个有机溴代化合物进行碳溴键均裂离解能的理论计算,得到5种密度泛函理论方法的计算值。将各种方法的计算结果与实验值进行比较研究后,得出最佳的计算键离解能的方法。用选定的最合适方法计算和预测更多溴代物的C-Br键离解能,并对有机溴化物中碳溴键的均裂离解能与化合物的空间结构之间的构效关系进行分析。结果表明,用BMK方法计算得到的碳溴键均裂离解能计算的标准偏差仅为4.76 kJ/mol,计算精度最高。     

有机化合物中C-I键均裂离解焓的精确预测及构效分析

运用7种密度泛函理论方法(PBEPBE、B3P86、BMK、B3PW91、M05、M06和M06-2X)分别对10个具有代表性且已有BDE实验值的有机碘代化合物进行碳碘键均裂离解焓的理论计算,得到7种密度泛函理论方法的计算值。将这些数据与实验值比较,得出最精确且符合计算精度要求的计算键离解焓的方法。用所筛选出来的最合适方法计算更多有机碘化物的C-I键均裂离解焓,并在计算结果的基础上对碘化物的分子结构与C-I键能之间的构效关系进行分析,寻找结构-键能之间的规律。     

煤及油母中常见C—X(X=N,S)的解离能

煤及油页岩中除了碳、氢和氧原子是主要的组成元素外,氮和硫等杂原子大都以C—X(X=N,S)的键合形式存在,在其结构及转化利用中同样发挥重要的作用。认识C—X的解离能,有助于建立氮、硫热解过程中的迁移模型,丰富对煤及油母中常见化学键性质的认识,对发展高效清洁的能源利用技术至关重要。利用双杂化密度泛函方法,系统研究了煤及油母中典型C—X键的解离能(BDE)范围。研究结果表明,煤及油母中常见C—N和C—S键的BDE值范围分别是154.1~55.7 kcal·mol~(-1)和83.0~56.6 kcal·mol~(-1)。在热解过程中,苯硫类自由基以及苯胺类自由基会在初期产生,其次才是巯基、胺类自由基等侧链取代自由基脱落。C—S键的整体BDE值范围比其他类型化学键更低,各类化学键最低BDE值的高低顺序符合O—HC—HC—CC—NC—SC—O的规律,其中,只有当有PhO·生成时,C—SC—O,否则C—OC—S。     

CuCl_2对石油稠油O—H…X(X=N,O,S)氢键削弱的量化计算研究

稠油分子间存在大量O—H…X(X=N,O,S)氢键,造成其分子间作用力和黏度较大,以过渡金属化合物为催化剂来削弱氢键是降低分子间作用力的主要方法。采用密度泛函理论B3LYP方法,使用Gaussian 03程序,以Cu Cl2作催化剂,对稠油间Cu Cl2—O—H…X(X=N,O,S)氢键的攻击削弱进行了计算。结果表明,Cu Cl2不仅增加了氢键的键长,使N,O,S的净电荷发生了转移,还使得系统的前线能隙下降,从而有效削弱了氢键。     

过氧化麦角甾醇分子的密度泛函理论研究

采用密度泛函理论(DFT)方法,在B3LYP/6-311+G(2d,p)水平上对过氧化麦角甾醇进行了计算研究。优化得到了过氧化麦角甾醇分子的结构,给出了分子的键长、键角、二面角等参数,并对其进行了1HNMR光谱、IR光谱、UV-Vis光谱理论模拟和自然电荷分析。自然电荷计算表明,羟基O和H原子很可能是关键的活性中心。理论计算结果与实验值符合的很好。     

NO2硝化正己烷及其理论计算

对NO₂硝化正己烷的反应进行了研究,分别考察了反应温度、摩尔比和反应时间的影响。结果表明：在反应温度为120℃、正己烷与NO₂摩尔比为1∶2、反应时间为4h的反应条件下,正己烷转化率可达85.9%。通过密度泛函理论（DFT）研究了NO₂硝化正己烷的反应机理,在B3LYP/6-311++G(3df,2pd)//B3LYP/6-31G*计算水平下精确计算了三个可能反应途径的活化能（E_a）。计算结果表明：该反应决速步骤为NO₂中O原子进攻正己烷中的H原子,其中2-硝基己烷和3-硝基己烷为主要产物,且计算结果与实验结果一致。分子几何结构、原子电荷和IR振动频率的数据表明C—H键的断裂和N—H键的形成是一个协同过程,参与硝化反应的原子C(5)、H(7)、O(22)、O(23)和N(21)的分子几何参数及其原子电荷有明显的变化。     

NiO(111)表面重构对乙烷C—H键活化影响的DFT+U研究

采用密度泛函理论(DFT)和Hubbard U值校正方法研究NiO(111)表面重构及其对乙烷C—H键断裂的影响。通过电子局域函数(Electron Localization Function,ELF)、态密度(Density of states,DOS)、过渡态结构和Bader charge等对表面重构和乙烷C—H键活化进行分析。结果表明,重构表面相比于理想表面更加稳定,同时重构表面上C—H键的活化更加困难。     

一种含氟含碘尿素衍生物对氯离子识别作用的模拟研究

采用B3LYP方法模拟研究了尿素无氟(A)及含氟(B)含碘衍生物对Cl-的识别机理,结果表明尿素衍生物受体分子A及B分别以其结构中的2个N—H键和2个C—I键与卤素阴离子间形成4个弱键进行识别.对于A┅Cl-体系,识别作用包括2个N—H┅Cl-红移氢键和2个C—I┅Cl-蓝移卤键弱相互作用;对于B┅Cl-体系,识别作用包括2个N—H┅Cl-红移氢键和2个C—I┅Cl-红移卤键弱相互作用;在A┅Cl-和B┅Cl-识别体系中相互作用能ΔEcp分别为-121.78和-179.71kJ/mol,即含氟受体B对Cl-具有较好的识别能力.     

基于密度泛函理论的普克鲁胺分子反应活性位点预测

基于量子化学密度泛函理论，对普克鲁胺分子表面静电势、平均局部离子化能、前线分子轨道、原子电荷及概念密度泛函活性指数进行计算分析。结果显示：普克鲁胺分子噁唑环双键原子平均局部离子化能较小，为HOMO轨道，f^-值较大；氰基N(8)原子附近存在分子表面静电势较小的极值点，较小原子电荷值，f^-值较大；咪唑环C(15)、嘧啶环H(38)附近存在分子表面静电势较大的极值点。研究表明：普克鲁胺分子噁唑环双键及氰基为亲电反应活性位点，苯环C(4)为亲核反应活性位点。氰基N(8)、咪唑环C(15)、嘧啶环H(38)在以静电吸引为主的反应中将发挥主要作用。     

富氮含能晶体4-氨基-3,7-二硝基三唑-[5,1,c][1,2,4]三嗪高压行为的密度泛函研究（英文）

采用周期性密度泛函理论(DFT)的GGA/PBE-G06方法研究了富氮含能晶体4-氨基-3,7-二硝基三唑-[5,1,c][1,2,4]三嗪(DPX-26)在静水压0～130 GPa范围内的高压行为。通过计算晶格参数(a、b、c)、键长、带隙(ΔE_g)和态密度(DOS),分析了DPX-26的晶体结构、分子结构和电子结构随压力的变化情况。结果表明,DPX-26晶体在81、82和92GPa发生3次显著的结构转变。81GPa时,分子间六元环破裂;在82GPa,C4—N7键拉长,三唑环严重扭曲并解离,N4—H6键拉长至0.1507nm,共价作用转变为氢键作用;92GPa时,C4—N7键键长从0.2324nm减小至0.1333nm,三唑环再次形成。压力增加导致体系离域性增强。     

Ab initio crystal structure and charge density distribution of a highly energetic 2,4-dinitrobenzoic acid molecule

The energetic parameters, such as density, bond strength, and sensitivity of explosives/ propellants decide their detonation power and safety. Experimentally, optimization of these parameters is found to be a difficult task; therefore, prior to synthesis, it makes sense to estimate these parameters by computational techniques, ab initio crystal structure prediction, and quantum chemical calculation coupled with the AIM analysis. Here, we predict the density of an energetic 2,4-dinitrobenzoic acid (DNBA) molecule from different ab initio crystal structure models and validate the results through comparisons with experimental data. The bond topological characterization reveals that the C NO₂ bonds are the weakest bonds and are identified as sensitive bonds in the molecule. The bond sensitivity is estimated from Murray’s method. The impact sensitivity of this molecule is also calculated. Large negative electrostatic potential regions are found near the NO₂ and carboxylic groups, which are the reactive sites of the molecule.     

Electronic structure evidence for all‐trans poly(methylvinylidene cyanide)

On the basis of a comparison of theoretical quantum calculations, by both semiempirical and ab initio methods, with photoemission and inverse photoemission results, we suggest that polymethylvinylidenecyanide (PMVC) adopts an all‐trans conformation with few, if any, alternating trans‐gauche carbon–carbon bond arrangements. The comparison of theory with the available photoemission and inverse photoemission excludes the presence of a significant fraction of gauche bonds in the polymer chains, indicative of the all‐trans conformation, with dipoles all aligned. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Experimental and quantum chemical studies of the effect of poly ethylene glycol as corrosion inhibitors of aluminum surface

The corrosion inhibition of poly ethylene glycol (PEG) toward the aluminum surface in 1.0 M HCl has been studied by weight loss and polarization techniques. The results showed that the PEG acts as a good inhibitor and the inhibition efficiency is due to the anodic and cathodic inhibition (mixed type). The thermodynamic functions were calculated to find a good correlation with the inhibition efficiency. Quantum chemical parameters were calculated using ab initio and DFT methods to find a good correlation with the inhibition efficiency. A good correlation was found between the theoretical calculations and experimental observations.     

Synthesis and Ab Initio/DFT Studies on 2-(4-methoxyphenyl)benzo[d]thiazole

2-aminothiophenol and 4-methoxybenzaldehyde were cyclized under microwave irridation and solvent free conditions to synthesize 2-(4-methoxyphenyl)benzo[d]thiazole. The molecular structure and vibrational frequencies of the title compound in the ground state have been investigated with ab initio (HF) and density functional theory methods (BLYP, B3LYP, B3PW91 and mPW1PW91) implementing the standard 6–311G(d,p) basis set. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.     

Hydrogen bond connectivity in jennite from ab initio simulations

The protonation scheme and the hydrogen bond connectivity in the structure of jennite were investigated by ab initio molecular dynamics simulations. The calculated statistics of hydrogen bonds at ambient conditions is consistent with the protonation scheme proposed by Bonaccorsi et al. (2004) based on the bond valence theory. The protons in the system are associated with the 2Ca–OH linkage and H₂O molecules. The dangling Si–O bond on the bridging tetrahedra is de-protonated. The proton dynamics revealed in the molecular dynamic simulations explains the apparent discrepancies in the NMR and X-ray diffraction studies of jennite.     

First Principles Investigation of Cold Curves of Metals

The rapid development of better high pressure experimental techniques combined with efficient and accurate density functional calculations of the structural properties of materials provide a new avenue to promote the study of materials at high pressures, which is currently based mostly on simple phenomenological modelling. The progress of experimental results into higher-pressure regimes represents a challenge to the phenomenological approaches, which can be addressed by carefully considered ab initio calculations. We present cold curves of several elements, calculated using different approximations of DFT and compare them with available experimental data. The comparison shows good agreement both in simple single phase and complex multi-phase cases. It suggests that DFT may be used to extrapolate high pressure behaviour of materials beyond the currently possible pressure range, with a robust estimate of the accuracy of the extrapolation based on various DFT implementations.     

Density functional theory studies of zeolite structure,acidity, and reactivity

Our recent application of quantum mechanical methods to the study of heterogeneous catalysis in zeolites is reviewed. We show that density functional theory (DFT) is a powerful means by which zeolite structure, acidity, and reactivity can be elucidated. The relative accuracy of DFT is comparable to that of traditional ab initio molecular orbital methods. However, the computational requirements of DFT are much less, allowing us to efficiently study the large systems needed for the realistic modeling of zeolite catalysis. We also demonstrate how the coupling of theoretical and experimental studies can greatly aid our atomic-level understanding of catalytic processes. We briefly describe the technical details of DFT and the factors that influence the accuracy of the results. Examples of DFT applied to the structure and acidity of H-ZSM-5 and substituted analogs are presented, as well as a combined DFT and NMR study of Hammett indicators adsorbed on an H-ZSM-5 model. Finally, the H/D exchange mechanism for benzene on zeolites is presented, demonstrating the important role DFT plays in the study of zeolite reactivity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Role of interatomic bonding in the mechanical anisotropy and interlayer cohesion of CSH crystals

Atomic scale properties of calcium silicate hydrate (CSH), the main binding phase of hardened Portland cement, are not well understood. Over a century of intense research has identified almost 50 different crystalline CSH minerals which are mainly categorized by their Ca/Si ratio. The electronic structure and interatomic bonding in four major CSH crystalline phases with structures close to those found in hardened cement are investigated via ab initio methods. Our result reveals the critical role of hydrogen bonding and importance of specifying precise locations for water molecules. Quantitative analysis of contributions from different bond types to the overall cohesion shows that while the SiO covalent bonds dominate, the hydrogen bonding and CaO bonding are also very significant. Calculated results reveal the correlation between bond topology and interlayer cohesion. The overall bond order density (BOD) is found to be a more critical measure than the Ca/Si ratio in classifying different CSH crystals.     

ClCF+的电子结构与光解离通道

用ab initio分子轨道方法对正电子自由基ClCF^ 的电子机构，几何构型，振动频率，过滤态进行量子化学计算，内禀反应坐标法计算结果表明，对于ClCF^ 来说有三条可能的解离通道，从而从理论上验证了在轰击ClCF^ 后所产生的碎片中存在的Cl、CF^ 、F、CCl^ 等粒子。     

The energetic and electronic properties of atomic hydrogen on MgO(001) surface: Tight-binding and Ab initio calculations

We report the computational results of hydrogen adsorption atop Mg and O atoms on the MgO(001) surface, followed by its absorption under the target atoms, using two approaches: tight-binding and ab initio methods. We present the energetic and electronic aspects of these interactions and discuss the qualities of the non-self-consistent field tight-binding results compared with the ab initio results. There is the qualitative reproduction of ab initio results in the hydrogen adsorption phase on both types of ions. The tight-binding results are found to be more accurate in the hydrogen absorption phase than in the adsorption phase. In the adsorption calculations the introduction of the surface dipole term in the tight-binding total energy would be required to compensate for the absence of electronic relaxation in the MgO(001) surface.