非导电微球悬浊系的介电谱——弛豫机制的考察和界面信息的解析

研究了不同浓度电解质溶液中聚苯乙烯微球悬浊液的介电谱, 发现在40 Hz～110 MHz频率范围内出现了两个明显的弛豫. 在介电模型基础上对弛豫原因的理论分析结果表明, 千赫兹频域出现的弛豫是由粒子附近双电层中对离子的扩散所致, 兆赫兹附近出现的弛豫源于空间电荷在固/液界面的累积. 应用Hanai方法计算出体系内部的相参数, 获得了微球/溶液界面的电信息, 并给出了合理解释. 理论计算结果验证了模型和方法的适用性. 实验采用透析法调制样品, 有效地防止了体系内部粒子二次团聚的发生.     

硫化物在铂电极上电氧化时空动力学的模型模拟和分析(英文)

根据铂电极上硫化物电催化氧化的反应机理,本文提取动力学模型并利用数值模拟研究了N型负微分阻抗(N-NDR)振荡区域的电极表面时空反应动力学.在均相体系模拟中观察到电流简单振荡和复杂振荡,其来源于双电层电势自催化与传质限制和毒化物种吸附负反馈的相互耦合.为了更接近于真实体系,在模型中考虑了平行和垂直于电极表面两个方向的传质过程.模拟结果发现了与实验现象具有相同演化行为的复杂斑图,如行波和闪烁波;同时在传质耦合体系模拟中观察到双电层电势双臂螺旋波.本研究工作促进对电化学体系时空斑图的理解和预测.     

单分子层受限冰-水共存界线毛细波与固-液相变动力学

冰-水界面动力学性质在冰形核、生长、表界面熔化中扮演核心角色, 长期以来一直被广泛关注. 然而, 受限水体系中冰-水界面的动力学性质却鲜有报道. 本工作利用平衡态分子动力学模拟方法和受限固-液两相平衡模拟技术, 对两种水模型(恒定偶极矩、可极化)描述的单分子层受限冰-水两相平衡体系中的一维固-液界线开展研究. 通过对一维受限冰-水界线的追踪, 计算了其热涨落波动的振幅与时间自关联函数色散谱, 进而计算一系列固-液界线动力学性质. 冰-水界线波动在短波长区域复合了快、慢两种不同时间尺度的弛豫过程, 在长波长区域则由慢弛豫过程主导. 相比块体冰-水界面体系, 以Rayleigh波为主的高频微观物理过程更多地参与了一维冰-水界线的动力学弛豫. 我们发现冰-水界线波动弛豫特征衰减时间的波矢依赖关系符合现有固-液界面动力学理论, 但一维界线弛豫的特征衰减时间比二维界面体系低了一个数量级左右. 计算了两种水模型体系冰-水界线的动力学系数, 并与块体冰-水界面比较, 发现受限冰-水(固-液)界线动力学系数远高于块体冰-水界面体系. 我们推测水分子转动自由度在受限腔中被强烈压制可能是导致受限体系超快冰-水(固-液)相变速率的主要原因. 本工作将在受限水体系超快相变(储能、传感)器件的设计工作中提供一定的理论指导意义.     

铂电极BZ反应系双电层稀疏区中的Turing结构

将扩散流作为场函数, 考虑φ电势的空间分布, 建立了铂电极BZ反应系在双电层稀疏区的动力学演化机制, 确立了纳入稀疏区φ电势效应的反应-扩散型演化方程. 采用Boltzmann分布近似, 解决了演化方程中含φ电势的流项的线性化问题; 导出了可在算法上实现的三变量体系线性化算子本征值的解析形式. 分别以静态铂电极BZ反应系双电层稀疏区和对应的纯粹BZ反应系作为参考模型系, 分析了经空间对称性破缺产生Turing结构的参数范围. 数值模拟发现, φ电场的存在使铂电极BZ反应系的输运过程在静态双电层稀疏区趋于电化学平衡时, 在对应的纯粹BZ反应体系中可呈现的Turing结构已趋于消失; 而在电流强度不太大的恒流不可逆铂电极BZ反应体系双电层稀疏区中, 鲜明稳定的Turing结构又重新出现在原参数区间内. 同时, 在静态双电层稀疏区不出现Turing结构的参数范围内也可找到类似的恒流稳定空间结构.     

离子交换树脂悬浊液的介电弛豫谱研究

研究了D354阴离子交换树脂分散在不同浓度KCl溶液中的悬浊液的频率域介电谱,发现在测量频率为106～107 Hz处出现了显著的介电弛豫现象,得出了介电常数、电导率以及弛豫时间随KCl溶液浓度的特异的变化关系,理论分析表明,该弛豫是一个以界面极化为主的非单一极化机制的弛豫过程,进而利用Maxwell-Wagner界面极化理论和双电层性质解释了该体系的特异介电行为,得到了树脂悬浊液在外加交变电场下的离子迁移和聚集信息,并确定了该树脂在静态平衡下双电层中对离子的相对离子强度.     

二氧化钛与水界面的理论研究进展

二氧化钛(TiO2)具有优良的电学性能和独特的光学性质,在光学材料、光电化学和光电池、光催化和环境治理等方面具有广泛的应用前景.然而,这些功能的实现都离不开周围的水环境,因此关于TiO2与水界面相互作用问题的研究至关重要.随着当前理论计算方法和计算机计算能力的提高,人们可以在原子层次来深入讨论和理解TiO2与水界面问题.采用第一性原理的量子化学计算方法,可以研究和解决TiO2与水界面的一些根本问题,如界面处水分子吸附结构和水分子与TiO2表面相互作用动力学行为.本文中,我们系统回顾了TiO2与水界面的第一原理计算的研究进展,并展望了固液界面理论计算模拟领域的发展前景.     

放射性核素在固-液界面上的吸附：模型及其应用

放射性核素在固-液界面上的吸附行为是其在低浓度下物理化学行为研究的重要内容之一。本文综述了固-液界面吸附研究方面取得的主要进展,总结了放射性核素在固-液界面的吸附动力学、热力学模型,重点讨论了表面配位模型和亚稳态理论在固-液界面吸附行为研究中的应用和发展,较为详细地概括了部分先进光谱技术、理论计算方法和模型模拟手段等在...     

3-氨基-1,2,4-三氮唑自组装膜对黄铜的缓蚀作用

3-氨基-1,2,4-三氮唑(ATA)是一种环境友好型金属处理剂, 以其在黄铜表面制备了自组装单分子膜(SAMs), 用电化学方法研究ATA SAMs对黄铜的缓蚀作用及其吸附行为. 结果表明, ATA分子易在黄铜表面形成稳定的ATA SAMs, SAMs抑制了黄铜的阳极氧化过程, 改变了电极表面的双电层结构, 固/液界面双电层电容明显降低, 有良好的缓蚀效果. 研究结果还表明, ATA的吸附行为符合Langmuir吸附等温式, 吸附机理是典型的化学吸附.     

CH_2Cl_2对离子液体BmimPF_6中二茂铁电化学行为的影响

应用循环伏安和交流阻抗法研究有机溶剂二氯甲烷对二茂铁在离子液体1-丁基-3-甲基咪唑六氟磷酸盐(Bm imPF6)中电化学行为的影响.实验表明,二氯甲烷可促进离子液体的离子解离,减小离子液体粘度,增加离子液体电导率,加速二茂铁在离子液体中的扩散,增大氧化还原峰电流.由于电极界面双电层结构的变化,导致双电层电容增大,电极反应电阻减小,从而加速了界面电子传递反应.     

薄层法研究十二烷基苯磺酸钠对硝基苯/水界面电子转移的影响

用薄层法研究了阴离子表面活性剂十二烷基苯磺酸钠(SDBS)对硝基苯/水界面电子转移的影响. 实验结果表明, 随着水相中十二烷基苯磺酸钠浓度的增加, 有机相中十甲基二茂铁(DMFc)和水相中Fe(CN)₆^3-发生的界面双分子反应的阴极平台电流呈现递减趋势, 但是界面双分子反应速率常数却呈递增趋势. 这是由于阴离子表面活性剂十二烷基苯磺酸钠在硝基苯/水界面形成了修饰层, 影响了界面双电层结构. SDBS在液/液界面的吸附为Langmuir吸附.     

Grand canonical ensemble approach to electrochemical thermodynamics,kinetics, and model Hamiltonians

The unique feature of electrochemistry is the ability to control reaction thermodynamics and kinetics by the application of electrode potential. Recently, theoretical methods and computational approaches within the grand canonical ensemble (GCE) have enabled to explicitly include and control the electrode potential in first principles calculations. In this review, recent advances and future promises of GCE density functional theory and rate theory are discussed. Particular focus is devoted to considering how the GCE methods either by themselves or combined with model Hamiltonians can be used to address intricate phenomena such as solvent/electrolyte effects and nuclear quantum effects to provide a detailed understanding of electrochemical reactions and interfaces.     

Examining the robustness of first-principles calculations for metal hydride reaction thermodynamics by detection of metastable reaction pathways

First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H(2) storage applications. Standard methods for this task efficiently identify the lowest energy reaction mechanisms among all possible reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying reactions that are metastable relative to the lowest energy reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step reactions identified in our recent work that examined reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218].     

Theoretical studies on the reactivity of molybdenum enzymes

In recent years, advances in theoretical methods and computational capabilities have made it possible to investigate reaction mechanisms in enzymes. Density functional theory (DFT) is commonly used to study reactions in model systems, while combined quantum mechanical/molecular mechanical (QM/MM) approaches allow the treatment of the complete solvated enzyme and thus provide insight into the mechanistic influence of the protein environment. This review starts with a brief overview over the available DFT and QM/MM methodology and then summarizes recent theoretical studies on biocatalysis by molybdenum-containing enzymes. It focuses on the reactions in members of the dimethylsulfoxide reductase, sulfite oxidase, and xanthine oxidase families, with special emphasis on the QM/MM studies of the latter. It concludes with a brief survey of theoretical work on some other molybdenum- and tungsten-containing enzymes.     

A Theoretical Study on Chapman Rearrangement

Some Chapman rearrangements are investigated using HF and B3LYP methods combined with two different basis sets (6‐31G** and 6‐31++G**) and both finite difference model and Janak's approximation. It is shown that although minimum polarizability (MPP) and maximum hardness (MHP) principles are always valid in these reactions, minimum electrophilicity principle (MEP) is followed just when DFT method (B3LYP) is used. The Morrel's rules are also successfully applied in predicting the validity of MEP in these rearrangements. Therefore, it seems that in the study of this kind of reaction, the results of DFT are more reliable than those of HF.     

Density functional studies on the Nazarov reaction involving cyclic systems

Density functional theory (DFT) has been used to define the energy profiles of the Nazarov reaction involving cyclic systems. The calculations were carried out at the B3LYP/6-311G** level of theory and the solvent (dichloromethane) contribution was estimated by using the recently developed SM5.43R solvation model. DFT calculations were first carried out to determine the energy profiles associated with the electrocyclization reactions of 3-hydroxy- and 3-ethoxypentadienyl cations in which one of the double bonds is embedded in O-heterocyclic and carbocyclic systems. In particular, the effects on the reaction rate of modifications to the substrate, as well as the presence of the heteroatom in the cycle, have been investigated. The torquoselectivity of the electrocyclization reaction was then explored with substituted O-heterocycles to understand the factors that control the stereochemical outcome of the process that preferentially provides 2,5-trans-disubstituted products. These DFT-based results rationally explain most of the experimental observations related to the Nazarov reaction of the substrates herein investigated and could be useful in the rational interpretation, and likely in the prediction, of the outcome of Nazarov reactions involving other cyclic systems.     

Electrochemical reactions at the electrode/solution interface:Theory and applications to water electrolysis and oxygen reduction

Theoretical simulations on complex electrochemical processes have been developed on the basis of the understanding in electrochemistry,which has benefited from quantum mechanics calculations.This article reviews the recent progress on the theory and applications in electrocatalysis.Two representative reactions,namely water electrolysis and oxygen reduction,are selected to illustrate how the theoretical methods are applied to electrocatalytic reactions.The microscopic nature of these electrochemical reaction...     

Metal-mediated reaction modeled on nature: the activation of isothiocyanates initiated by zinc thiolate complexes

On the basis of detailed theoretical studies of the mode of action of carbonic anhydrase (CA) and models resembling only its reactive core, a complete computational pathway analysis of the reaction between several isothiocyanates and methyl mercaptan activated by a thiolate-bearing model complex [Zn(NH(3))(3)SMe](+) was performed at a high level of density functional theory (DFT). Furthermore, model reactions have been studied in the experiment using relatively stable zinc complexes and have been investigated by gas chromatography/mass spectrometry and Raman spectroscopy. The model complexes used in the experiment are based upon the well-known azamacrocyclic ligand family ([12]aneN(4), [14]aneN(4), i-[14]aneN(4), and [15]aneN(4)) and are commonly formulated as ([Zn([X]aneN(4))(SBn)]ClO(4). As predicted by our DFT calculations, all of these complexes are capable of insertion into the heterocumulene system. Raman spectroscopic investigations indicate that aryl-substituted isothiocyanates predominantly add to the C═N bond and that the size of the ring-shaped ligands of the zinc complex also has a very significant influence on the selectivity and on the reactivity as well. Unfortunately, the activated isothiocyanate is not able to add to the thiolate-corresponding mercaptan to invoke a CA analogous catalytic cycle. However, more reactive compounds such as methyl iodide can be incorporated. This work gives new insight into the mode of action and reaction path variants derived from the CA principles. Further, aspects of the reliability of DFT calculations concerning the prediction of the selectivity and reactivity are discussed. In addition, the presented synthetic pathways can offer a completely new access to a variety of dithiocarbamates.     

Assessing the validity of DLPNO-CCSD(T) in the calculation of activation and reaction energies of ubiquitous enzymatic reactions

The domain-based local pair natural orbital coupled-cluster with single, double, and perturbative triples excitation (DLPNO-CCSD(T)) method was employed to portray the activation and reaction energies of four ubiquitous enzymatic reactions, and its performance was confronted to CCSD(T)/complete basis set (CBS) to assess its accuracy and robustness in this specific field. The DLPNO-CCSD(T) results were also confronted to those of a set of density functionals (DFs) to understand the benefit of implementing this technique in enzymatic quantum mechanics/molecular mechanics (QM/MM) calculations as a second QM component, which is often treated with DF theory (DFT). On average, the DLPNO-CCSD(T)/aug-cc-pVTZ results were 0.51 kcal·mol⁻¹ apart from the canonic CCSD(T)/CBS, without noticeable biases toward any of the reactions under study. All DFs fell short to the DLPNO-CCSD(T), both in terms of accuracy and robustness, which suggests that this method is advantageous to characterize enzymatic reactions and that its use in QM/MM calculations, either alone or in conjugation with DFT, in a two-region QM layer (DLPNO-CCSD(T):DFT), should enhance the quality and faithfulness of the results.     

Hydrolysis of a two-membered silica ring on the amorphous silica surface

We have combined density functional theory (DFT) with classical interatomic potential functions to model hydrolysis of amorphous silica surfaces. The water-silica interaction is described by DFT with incorporation of a long-range elastic field described by classical interatomic potentials. Both physisorption and chemisorption of water on a surface site, known as the two-membered silica ring, are studied in detail. The hybrid quantum-mechanical and classical mechanical method enables more realistic treatment of chemical processes on an extended surface than previous methods. We have studied cooperative events in the hydrolytic reactions and discovered a new reaction pathway that involves a double proton transfer process. In addition, the evaluation of the total energy in a hybrid quantum-mechanical and classical mechanical system is discussed.     

Self-consistent combination of the three-dimensional RISM theory of molecular solvation with analytical gradients and the Amsterdam density functional package

The three-dimensional reference interaction site model with the closure relation by Kovalenko and Hirata (3D-RISM-KH) in combination with the density functional theory (DFT) method has been implemented in the Amsterdam density functional (ADF) software package. The analytical first derivatives of the free energy with respect to displacements of the solute nuclear coordinates have also been developed. This enables study of chemical reactions, including reaction coordinates and transition state search, with the molecular solvation described from the first principles. The method yields all of the features available by using other solvation approaches, for instance infrared spectra of solvated molecules. To evaluate the accuracy of the present method, test calculations have been carried out for a number of small molecules, including four glycine conformers, a set of small organic compounds, and carbon nanotubes of various lengths in aqueous solution. Our predictions for the solvation free energy agree well with other approaches as well as experiment. This new development makes it possible to calculate at modest computational cost the electronic properties and molecular solvation structure of a solute molecule in a given molecular liquid or mixture from the first principles.