从常温常压到超临界乙醇的分子动力学模拟

采用分子动力学方法系统地研究了从常温常压到超临界状态乙醇的热力学性质、结构性质和动力学性质.模拟发现随着温度的升高,体系焓值增大,乙醇分子间的氢键作用减弱,自扩散系数增大;随着压强的增大,乙醇分子间的氢键作用增强,自扩散系数减小;乙醇自扩散系数在液相区随温度变化不明显,在气相区随压强增大很快减小,超临界区乙醇的自扩散系数比液相区大十几倍.温度和压强对乙醇自扩散系数的影响可通过密度来体现.与常温常压相比,超临界条件下的乙醇体系因密度涨落存在分子聚集现象,且在低密度区域更显著;乙醇分子间的氢键作用明显减弱,结     

液态过渡金属Pd和Pt的结构与微观动力学行为

采用反映原子多体相互作用的镶嵌原子模型和有效偶势模型及分子动力学计算机模拟技术,研究了液态过渡金属Pd和Pt在熔点附近的结构与微观动力学行为。计算了Pd和Pt分别在1818和2037K时的双体分布函数、平均平方位移、自扩散系数和速度自相关函数,讨论了多体相互作用对上述各物理量的影响。结果表明,多体相互作用对液态Pd和Pt的局域结构影响较小,但对反映微观动力学行为的平均平方位移、自扩散系数和速度自相关函数的影响较大。 关键词：     

纳米铜团簇扩散性质研究

本文通过分子动力学模拟研究了纳米铜团簇的自扩散性质,结果表明Nc8949铜团簇自扩散系数随温度的升高而增大,在温度为1000 K时纳米铜团簇的扩散系数随团簇半径的倒数基本呈线性增加.同时指出在常温下团簇几乎无扩散行为,而某些文献中关于常温下晶粒扩散分子动力学模拟结果是模拟体系宏观转动造成的虚假现象.?     

骨架柔性对短链烷烃分子在金属-有机骨架材料中扩散的影响

采用分子动力学方法,对短链烷烃在柔性和刚性具有相似拓扑结构的金属有机骨架材料(isoreticular metal-organic frameworks, IRMOFs)中的分子扩散进行了研究. 结果表明,分子在柔性骨架中的自扩散系数大于在刚性骨架中的自扩散系数,在柔性骨架中的活化能小于在刚性骨架中的活化能. 骨架的柔性对自扩散系数的影响随着温度的升高而增加,随着扩散分子数目以及扩散分子链长的增长而降低. 因此,在利用分子模拟方法研究烷烃在金属-有机骨架材料中的扩散行为时,尤其对于较高温度以及较短的烷烃分 关键词： 分子模拟 金属-有机骨架材料 柔性骨架 扩散     

温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF_4]、[HPy][BF_4]、[OPy][BF_4]热力学性质的影响,得到了每个体系的密度、自扩散系数、电导率和黏度等.研究结果表明:随着温度升高,同一种离子液体的密度减小,阴阳离子的自扩散系数明显增大,电导率升高,而黏度降低.在同一温度下,随着阳离子上烷基链的增长,离子液体的密度减小,但热力学性质的变化规律并不完全同步.烷基链长最短的[BPy][BF_4]的自扩散系数和电导率在每个温度下均为最大,而黏度最小;但烷基碳链更长的[OPy][BF_4]和[HPy][BF_4]的各种性质相差不大,甚至当温度大于323 K时,烷基链较长的[OPy][BF_4]的自扩散系数比[HPy][BF_4]的大.     

温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF4]、[HPy][BF4]、[OPy][BF4]热力学性质的影响, 得到了每个体系的密度、自扩散系数、电导率和黏度等. 研究结果表明: 随着温度升高, 同一种离子液体的密度减小, 阴阳离子的自扩散系数明显增大, 电导率升高, 而黏度降低. 在同一温度下, 随着阳离子上烷基链的增长, 离子液体的密度减小, 但热力学性质的变化规律并不完全同步. 烷基链长最短的[BPy][BF4]的自扩散系数和电导率在每个温度下均为最大, 而黏度最小; 但烷基碳链更长的[OPy][BF4]和[HPy][BF4]的各种性质相差不大,甚至当温度大于323K时, 烷基链较长的[OPy][BF4]的自扩散系数比[HPy][BF4]的大.     

液态Co物性的平衡及非平衡分子动力学模拟

本文采用EAM作用势,通过平衡分子动力学(EMD)模拟的方法计算了Co熔体的自扩散系数、剪切粘度等物理性质.同时采用非平衡分子动力学(NEMD)方法计算了Co的剪切粘度.研究表明有关传输性质的计算是可与实验比较的,能够反映出液态Co典型的动力学特性.     

模拟扩散系数的分子动力学方法

在分析当前应用的各类分子动力学方法的基础上提出一个2参数(即温度松弛时间和压力松弛时间)模型,采用正交实验确定了最优的模型参数,压力与温度松弛时间的最优值均为2fs.在最优条件下跟踪系统的体积变化,最大波动在10%之内.将该模型应用于不同温度下氩及超临界二氧化碳自扩散系数模拟,并用动力学理论对自扩散系数与温度、压力的关系进行了定性分析,结果与实验值吻合.说明新模型具有稳定而准确的特点.     

纳米受限效应下流体自扩散机理及规律研究

当固体壁面间距仅有几个纳米时,纳米受限效应使得流体自扩散系数降低1²个数量级,孔径、温度和压力的影响显著且复杂。分析受限流体扩散机理和规律,建立简洁的关联式具有重要意义。本研究从分子模拟出发,经过仔细计算和分析,获得了大量纳米孔隙中流体自扩散系数数据。分析了壁面吸附作用对流体扩散的影响机理和规律,提出了可简单描述流体扩散行为的无量纲扩散系数,从而与努森数建立相应关联式,具有较强的适用性。     

LiCl玻璃急冷过程的分子动力学计算机模拟研究

用分子动力学方法对LiCl玻璃的急冷过程进行了计算机模拟。计算了急冷过程中各温度模拟体系的径向分布函数、配位数和Li⁺,Cl^-的自扩散系数。对模拟体系的键角进行了统计。讨论了不同温度下系统中微观空孔的分布。计算和分析清楚地表明模拟系统的玻璃态转变温度为498—298K。 关键词：     

Self-diffusion in liquid lithium and lead from coherent quasi-elastic neutron scattering data

The temperature dependence of the self-diffusion coefficient of liquid lithium in the temperature range of 500–830 K has been investigated using coherent quasi-elastic neutron scattering. Good agreement with the results obtained from incoherent quasi-elastic neutron scattering experiments traditionally used for this purpose has been achieved, as well as with the corresponding literature data. In addition, one temperature point (623 K) has been obtained for the self-diffusion coefficient of liquid lead, which is a pure coherent scatterer.     

Peculiarities of self-diffusion of alkane molecules in kaolinite

Self-diffusion of alkanes in kaolinite has been explored by pulsed field gradient nuclear magnetic resonance. The concentration dependences of average self-diffusion coefficient (SDC) of liquid have been studied in the wide temperature interval (T=253?383 K). The translational mobility of alkane molecules in kaolinite was shown to have some specific peculiarities. An anomalous rise was found in the average self-diffusion coefficient of the liquid as its content in kaolinite decreased. To explain this we should introduce a new “gas-like” state for the diffusant, whose mobility exceeds that of pure liquid. The possibility of the existence of such a state is explained by kaolinite’s ability to increase the specific surface area of the induced liquid. Analysis of a shape of the spin-echo diffusion attenuation leads one to suppose that there are heterogeneities in the medium’s porous space.     

Molecular collisions and self-diffusion in liquids

The velocity autocorrelation function and coefficient of self-diffusion are derived for a hard-sphere fluid. An earlier quasi-lattice model of self-diffusion in liquids is re-examined and a less restrictive expression for the self-diffusion coefficient is derived. The coefficient of self-diffusion of a light or heavy isotope in the normal liquid is considered both for hard spheres and in the quasi-lattice approximation. An experiment is proposed to clarify the nature of the isotope effect in self-diffusion.     

Relation between self-diffusion and viscosity in dense liquids: new experimental results from electrostatic levitation

By using the technique of electrostatic levitation, the Ni self-diffusion, density, and viscosity of liquid Zr(64)Ni(36) have been measured in situ with high precision and accuracy. The inverse of the viscosity, η, measured via the oscillating drop technique, and the self-diffusion coefficient D, obtained from quasielastic neutron scattering experiments, exhibit the same temperature dependence over 1.5 orders of magnitude and in a broad temperature range spanning more than 800 K. It was found that Dη=const for the entire temperature range, contradicting the Stokes-Einstein relation.     

Study of molecular mobility of fluid in zeolite NaX.

The self-diffusion of n-decane in zeolite NaX was studied by NMR PFG method. The situation when the liquid was only in the crystalline channels was studied in details. The restricted molecular motion of liquid in the crystalline channels was observed. The reasons of the anomalous self-diffusion of n-decane in zeolite bed were stated. The technique of the determination of the genuine self-diffusion coefficient in such porous systems was proposed. The genuine self-diffusion coefficients for system NaX/n-decane were obtained.     

Structure and effective interionic potential of liquid palladium,platinum and zirconium

The structure of palladium, platinum and zirconium in the liquid state has been studied by X-ray diffraction near the melting point. In all the cases the structure factor looks similar to those of liquid metals such as copper and silver in contrast to mercury, tin and bismuth which show the small hump or the large asymmetry of the first peak maximum in the structure factor. The atomic radial distribution function was evaluated from the structure factor and the interatomic distance and coordination number of each liquid metal were also obtained. The effective interionic potential was derived from the structural data obtained in this work using the Born-Green equation and applied to the estimation of self-diffusion coefficient and viscosity coefficient in these liquid metals by the kinetic theory of fluids.     

Microscopic properties of liquid gallium from quasi-elastic neutron scattering experiments

The results of the neutron diffraction study of liquid gallium on the DIN-2PI spectrometer (IBR-2 reactor, JINR, Dubna) have been discussed. The analysis of the experimental data has provided temperature dependences of diffusion and relaxation characteristics of liquid gallium in the temperature range of 313–793 K. It has been found that an increase in the temperature is accompanied by the gradual deviation of the temperature dependence of the self-diffusion coefficient from the known dependences obtained from the data on viscosity. Such a behavior is explained by the beginning clustering of liquid gallium induced by the prevailing covalent character of interatomic bonds.     

Using the Ab Initio Molecular Dynamics Method for Simulating the Peculiarities in the Temperature Dependence of Liquid Bismuth Properties

The specific features pertinent to the temperature dependence of the electronic and atomic properties of liquid bismuth that have been observed in experiments are investigated according to the ab initio molecular dynamics method using the SIESTA open software package. The density of electronic states, the radial distribution function of atoms, and the self-diffusion coefficient are calculated for the temperature range from the melting point equal to 545 K to 1500 K. The calculated data are in good agreement with the experimental data. It is found that the position of the first peak in the radial distribution function of atoms and the self-diffusion coefficient are characterized by a nonmonotonic dependence under the conditions of superheating by approximately 150 K above the melting temperature. In the authors’ opinion, this dependence feature is attributed to a change in the liquid short-range order structure.