烷基化芳胺润滑添加剂抗氧抗腐蚀机理的密度泛函理论研究

采用量子化学的密度泛函理论计算了8种烷基化芳胺抗氧抗腐蚀添加剂与烷氧自由基(C6H13O·)的结合能以及与铁原子簇的化学吸附作用能,探讨了化合物的结构特征、作用机理、授受电子的性质和取代基效应.结果表明:这些添加剂的HOMO均为带有杂原子的孤对电子的π-分子轨道,HOMO可以与金属原子的LUMO发生相互作用,HOMO的电子转移到金属原子的LUMO上形成配位键和稳定的吸附态;添加剂的LUMO均为苯环的π-共轭体系组成,可与RO·的SOMO相互作用,LUMO接受RO·的电子生成稳定的加成产物,添加剂具有授受电子性质;烷基化芳胺添加剂抗氧抗腐蚀性能与取代基的供电子效应或共轭效应有关,当供电子效应强时可以增加添加剂与RO·的结合能以及与铁原子簇的化学吸附作用能.依据计算结果可以推测8种化合物的抗氧抗腐性能由高到低顺序为:化合物Ⅰ＞Ⅵ＞Ⅷ＞Ⅶ＞Ⅲ＞Ⅴ＞Ⅳ＞Ⅱ,计算结果与实验结果一致.     

水在β-氮化硅(0001)面吸附的密度泛函理论研究

采用密度泛函理论(DFT)的B3LYP方法对H2O在β-Si3N4(0001)面上的吸附进行研究,采用原子簇模拟β-Si3N4(0001)表面,在6-31G·水平上计算常温常压下H2O分子在β-Si3N4(0001)表面的吸附构型和吸附能及电荷变化,同时考察温度、压强及预吸附BH3对吸附体系的影响.结果表明:H2O分子通过H原子吸附在β-Si3N4(0001)面的N原子顶位时最有利;当温度为100 ℃,压强分别为3×105～10×105 Pa时,吸附能为189.59 kJ/mol,与常温常压体系相比,吸附能增加了57.19 kJ/mol,吸附后O-H键拉长,可能发生解离;在BH3修饰的β-Si3N4(0001)表面上,由于预吸附导致吸附能减少.     

Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

A density functional theory (DFT) study has been carried out for [Znn-1Al(OH2)n+6(OH)2n-2]3+(n=3-6) and [Znn-1 Al(OH2)2n-2(OH)2n-2 ]3+ (n=7) clusters,which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides (LDHs) with Zn/Al molar ratio (R) in the range 2-6,in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs.Based on systematic calculations of the geometric parameters and formation energies of the cluster models,it was found that it is possible for Zn2+ and Al3+ cations to replace Mg2+ isomorphously in the brucite-like structure with different R values,resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs.Analysis of the geometry and bonding around the trivalent Al3+ or divalent Zn2+ cations reveals that Al3+ plays a more significant role than Zn2+ in determining the microstructure properties,formation and bonding stability of the corresponding ZnRAl clusters when R＜5,while the influence of Zn2+ becomes the dominant factor in the case of R≥5.These findings are in good agreement with experiments.This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.     

Cyclic density functional theory: A route to the first principles simulation of bending in nanostructures

We formulate and implement Cyclic Density Functional Theory (Cyclic DFT) — a self-consistent first principles simulation method for nanostructures with cyclic symmetries. Using arguments based on Group Representation Theory, we rigorously demonstrate that the Kohn-Sham eigenvalue problem for such systems can be reduced to a fundamental domain (or cyclic unit cell) augmented with cyclic-Bloch boundary conditions. Analogously, the equations of electrostatics appearing in Kohn-Sham theory can be reduced to the fundamental domain augmented with cyclic boundary conditions. By making use of this symmetry cell reduction, we show that the electronic ground-state energy and the Hellmann-Feynman forces on the atoms can be calculated using quantities defined over the fundamental domain. We develop a symmetry-adapted finite-difference discretization scheme to obtain a fully functional numerical realization of the proposed approach. We verify that our formulation and implementation of Cyclic DFT is both accurate and efficient through selected examples.The connection of cyclic symmetries with uniform bending deformations provides an elegant route to the ab-initio study of bending in nanostructures using Cyclic DFT. As a demonstration of this capability, we simulate the uniform bending of a silicene nanoribbon and obtain its energy-curvature relationship from first principles. A self-consistent ab-initio simulation of this nature is unprecedented and well outside the scope of any other systematic first principles method in existence. Our simulations reveal that the bending stiffness of the silicene nanoribbon is intermediate between that of graphene and molybdenum disulphide — a trend which can be ascribed to the variation in effective thickness of these materials. We describe several future avenues and applications of Cyclic DFT, including its extension to the study of non-uniform bending deformations and its possible use in the study of the nanoscale flexoelectric effect.     

密度泛函理论派生概念和原理在摩擦化学中的应用

评述了密度泛函理论派生概念和原理在摩擦化学中的应用，指出可以采用摩擦化学势(或摩擦化学电负性)和摩擦化学硬度作为表征固体摩擦材料和润滑剂分子力化学反应活性的量化参数，从而为摩擦化学计算与设计提供量子化学参数。     

Correlation between the crossover modulus and the molecular weight distribution using the Doi-Edwards theory of reptation and the Rouse theory

The crossover modulus in the dynamic mechanical spectrum was linked with the molecular weight distribution (MWD) over a wide range of polydispersity ( = 1 to 6). Reasonable agreement was obtained between theory and experiment for near monodisperse and narrow MWD polymers using the Doi-Edwards theory of reptation. For broad MWD polymers, the Doi-Edwards theory was found to be inapplicable. Using the Doi-Edwards theory for the shorter chains and a Rouse type mechanism for the longer chains, a good fit was obtained between the calculated and experimentally measured crossover modulus values.     

Effect of the Nonmonotonic Temperature Dependence of Water Density on the Decay of an Initial Density Discontinuity

The effect of the nonmonotonic temperature dependence of water density on gravity current flow after removal of the shield which separated warm and cold water was studied experimentally. If the temperature of water of maximum density was in the interval between the initial temperatures on the different sides of the shield, Rayleigh-Taylor instability developed along with shear instability under normal conditions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 66–73, January–February, 2006.     

甲烷及其氟氯代物在TATB晶体表面吸附的模

采用Discover/MaterialStudio中的分子动力学方法(COMPASS力场、NVT)及结构优化方法,模拟了甲烷及其氟氯代物(共15种化合物)在TATB超胞的(001)、(100)及(010)晶面的吸附作用。结果表明:(1)TATB晶面与大多数分子相互作用的强弱次序为:(010)(100)(001),这可能与晶面结构差异及氢键的形成有关;(2)三种晶面上,吸附能最大(为负值)的都是CH4、CF4,表明如果氟聚合物中氢或氟的含量过高均可能导致聚合物与TATB相互作用减弱。     

基于小波理论的沥青路面稳态响应解析解研究

为了研究移动载荷作用下的沥青路面稳态响应,将沥青路面看作Kelvin粘弹性地基上不仅具有弹性,而且具有粘滞性的无限长梁,建立稳态响应计算的数学模型。利用Fourier变换和小波变换方法,得到了求解沥青路面稳态响应解析解的一种新方法,并进行了实例计算与分析。由于该方法不需要进行复杂的多重积分运算,计算快捷、方便,为研究沥青路面动力响应提供了一种有效算法。     

建筑结构基于巴斯金风速谱的系列风振响应的简明封闭解

针对巴斯金风速谱激励下的建筑结构顺风向振动响应表达式复杂的问题,提出了一种简明封闭解法.巴斯金随机谱广泛应用于描述脉动风、随机地震动和路面不平顺等各种随机激励,本文基于留数定理给出巴斯金风速功率谱的二次正交式.综合运用复模态法和虚拟激励法获得了建筑结构系列响应(位移、层间位移及其变化率)功率谱的统一形式的二次正交式,并根据谱矩的定义获得了建筑结构系列响应的方差和谱矩及绝对加速度方差的简明封闭解.运用本文方法对一8层建筑结构进行分析,并与传统虚拟激励法进行对比研究,表明本文所得封闭解正确,并可用于验证虚拟激励法在谱矩和方差分析时的精度和效率.由于本文方法含有复模态法,故可用于各类线性结构基于巴斯金谱的随机响应分析和基于动力可靠度及舒适度的动力优化分析.     

modeling of multicomponent multiphase mixture flows on the basis of the density-functional method

Examples of numerical calculations of isothermal flows of two-phase two-component mixtures based on the density-functional method are presented. Using this method, the following problems are calculated in the two-dimensional formulation: drop impact on a liquid layer, drop rupture in a Couette flowfield, wetting-angle formation for a drop on a solid surface, development of Rayleigh-Taylor and Kelvin-Helmholtz instability on a gas-liquid interface.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 101–114.Original Russian Text Copyright © 2004 by Demyanov and Dinariev.