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1.
提出了用于计算实际体系熵相关性质的Monte Carlo 多级取样分子模拟方法.应用这一方法,对硬球流体的化学势及Helmholtz 自由能进行了估算,得到了满意的结果.计算化学势时,不存在通常试验粒子方法所遇到的高密度问题.该方法特别适合规律性的系统研究,较之普通模拟方法要有效得多.模拟得到的硬球体系无限稀释组份的超额化学势与对比直径的关系,在相变区域为一条双凹曲线;无论是在相变区还是在单相区,Carnahan-Starling 公式对这一关系的描述均有较大偏差.  相似文献   

2.
AB2型聚合物流体的表面结构性质   总被引:1,自引:0,他引:1  
在密度泛函理论(DFT)框架下, 应用改进的基本度量理论(MFMT)表达硬球作用对自由能泛函的贡献, 根据统计力学理论结合加权密度近似(WDA)表达聚合作用对自由能泛函的贡献, 建立了描述AB2型聚合物流体的化学势, 得到了聚合物流体在硬球颗粒表面的密度分布表达式, 计算了聚合物流体在硬球颗粒表面附近的密度分布, 并探讨了体积分数、聚合程度和硬球颗粒尺度对体系密度分布的影响. 此外, 通过体系密度分布, 进一步分析了体积分数、聚合程度和硬球颗粒尺度与剩余吸附的关系.  相似文献   

3.
在密度泛函理论(DFT)框架下,应用改进的基本度量理论(MFMT)和统计力学理论结合加权密度近似(WDA)分别表示硬球作用和聚合作用对自由能泛函的贡献,建立了描述ABg型超支化聚合物流体的化学势,得到了聚合物流体在平行板间的密度分布表达式,计算了聚合物流体在两平行板间的密度分布,并探讨了体积分数、反应程度和单体中B类官能团数对体系密度分布的影响.此外,通过体系密度分布,进一步分析了反应程度、板间宽度与溶剂化力的关系.  相似文献   

4.
电解质模型流体的MonteCarlo分子模拟   总被引:2,自引:1,他引:1  
采用正则系综Monte Carlo分子模拟方法,模拟得到了一系列状态条件下1:1 价和2:2价对称电解质模型流体的径向分布函数、构型能和压缩因子的“机器实验 数据”,这些数据对构筑电解质溶液的新参考流体具有重要意义。模拟过程中,电 解质溶液被简化为硬球离子和硬球点偶扳子的混合物,离子—离子、离子—偶极和 偶极—偶极长程位能计算采用了Ewald求和方法。最后,对离子—偶极子混合物的 结构和热力学性质与体系温度、密度和浓度的关系进行了分析和讨论。  相似文献   

5.
殷开梁 《化学教育》2018,39(18):18-23
对化学势概念作了比较详细的解读,并结合扩散、相变化、渗透以及化学变化等过程,对化学势判据在这些过程中的应用给出了图文并茂的说明,借此充分阐述了化学势所体现的化学中变化趋势的这一势的含义。  相似文献   

6.
利用粒子交换分子动力学模拟方法(Particle exchange molecular dynamics,PEMD)研究了Lennard-Jones流体的气液相图.模拟中,用两个耦合箱分别代表液相和气相.通过直接比较两箱的粒子化学势来控制交换粒子,从而达到两相平衡.采用Widom方法计算化学势.两模拟箱平衡时具有相同的温度、压强和粒子化学势.模拟的气液相图结果与利用其它方法得到的Lennard-Jones流体气液相图符合得很好.  相似文献   

7.
聚乙二醇型聚氨酯软硬段对其相变储热性能的影响   总被引:2,自引:0,他引:2  
以不同分子量的聚乙二醇(PEG)为软段,MDI-BDO为硬段,采用两步法溶液聚合合成一种具有固-固相变储热性能的聚氨酯材料.通过DSC,WAXD等测试手段对体系的软硬段结晶性,微相分离,相变可逆性及循环热稳定性进行研究,结果表明,聚氨酯中硬段的存在对软段结晶有着很大的影响,当软段分子量达到2000或以上时,软段才具有较大的结晶度和熔融相变焓,且硬段含量必须高于一定值才能形成较为完善的物理交联网络以保证材料在发生相变时维持固体状态.同时符合这两个条件的试样能具有较好的固-固相变储热性能.就软段PEG含量及分子量对材料储热性能的影响进行了研究,通过调节软段含量与分子量得到一系列具有不同相变焓和相变温度的聚氨酯固-固相变储热材料.经测试还发现,该材料具备很好的相变可逆性和循环热稳定性,是一类很有开发前景的相变储热材料.  相似文献   

8.
在Barker Henderson, Zhang以及Wertheim 等微扰理论的基础上,以方阱势硬球流体为参考体系,将Zhang的解析表达方法与Wertheim 的链成键自由能的处理方法结合起来,推导出自由链接的链状分子流体的Helmholtz自由能的解析表达式,并得到了压缩因子、内能、恒容热容等热力学性质的计算式.计算结果与MC(Monte Carlo)模拟结果吻合良好.对Zhang的解析表达式与“TPT D”(二阶Wertheim微扰理论)的结合也作了推导和计算.  相似文献   

9.
约束条件下的硬球流体   总被引:1,自引:0,他引:1  
利用密度泛函理论和分子动力学方法,对处于两平行硬墙之间的硬球流体的密度分布进行了计算通过比较两种方法的结果,发现在墙之间距离较大时,Rosenfeld密度泛函理论的结果与分子动力学模拟的结果符合很好;当两堵墙间的距离很小时,这两个结果之间存在明显的不一致.另外,还研究了约束条件下密度分布的结构.  相似文献   

10.
将溶液中某组分化学势的计算方式归纳为两种:(1)利用气液平衡时,溶液中某组分的化学势和气相中该组分的化学势相等这一关系来计算;(2)利用溶液中某组分化学势的全微分表达式直接积分来计算。在此基础上,给出了渗透压公式的一种新推导方式,并指出部分物理化学教材关于渗透压定义(Π=p2-p1)的不合理性以及推导渗透压时存在的不妥之处。  相似文献   

11.
12.
New properties for the one particle bridge function B(1)(r), which are necessary to the calculation of the excess chemical potential betamue), are derived for the hard sphere fluid. The method, which only requires the knowledge of the bridge function B(2)(r), is based on an investigation of the correlation function dependence on the Kirkwood charging parameter. In this framework, the unavoidable question of topological homotopy is addressed. As far as B(2)(r) is considered as exact, this work provides useful information on B(1)(r) in the well identified dynamical regimes of the hard sphere fluid. Signatures of the transitions between these regimes are identified on the trends of B(1)(r). This approach provides self-consistent results for betamue) that agree very well with simulation data.  相似文献   

13.
Based on a new and consistent formulation of scaled particle theory for a fluid confined in random porous media, a series of new approximations are proposed and one of them gives equations of state with excellent accuracy for a hard sphere fluid adsorbed in a hard sphere or an overlapping hard sphere matrix. Although the initial motivation was to remedy a flaw in a previous formulation of the scaled particle theory for a confined fluid, the new formulation is not a trivial and straightforward correction of the previous one. A few conceptual and significant modifications have to be introduced for developing the present formulation.  相似文献   

14.
An equation of state for the multicomponent fluid phase of nonattracting rigid particles of arbitrary shape is presented. The equation is a generalization of a previously presented equation of state for pure fluids of rigid particles; the approach describes the volumetric properties of a pure fluid in terms of a shape factor, zeta, which can be back calculated by scaling the volumetric properties of pure fluids to that of a hard sphere. The performance of the proposed equation is tested against mixtures of chain fluids immersed in a "monomeric" solvent of hard spheres of equal and different sizes. Extensive new Monte Carlo simulation data are presented for 19 binary mixtures of hard homonuclear tangent freely-jointed hard sphere chains (pearl-necklace) of various lengths (three to five segments), with spheres of several size ratios and at various compositions. The performance of the proposed equation is compared to the hard-sphere SAFT approach and found to be of comparable accuracy. The equation proposed is further tested for mixtures of spheres with spherocylinders. In all cases, the equation proved to be accurate and simple to use.  相似文献   

15.
We consider a model for adsorption of a simple fluid in disordered polydisperse adsorbents. The fluid consists of hard sphere particles. On the other hand, the adsorbents of this study are modeled as a collection of hard spheres with their diameter obeying a certain distribution function. Our focus is in the evaluation of the chemical potential of the fluid immersed in such a polydisperse material. It permits us to obtain porosity and pore size distribution for the adsorbent, as well as a set of adsorption isotherms. The latter have been calculated theoretically and by grand canonical Monte Carlo simulations. We observe that the width of assumed polydispersity distribution affects all the properties of the system. Nevertheless, the effect of matrix packing is dominant in determining adsorption for this class of models. We are convinced that the matrix structures generated via more sophisticated algorithms would exhibit stronger effects of polydispersity on the entire set of properties of adsorbed simple fluids.  相似文献   

16.
Results are presented of a systematic study of the transport properties of the rough hard sphere fluid. The rough hard sphere fluid is a simple model consisting of spherical particles that exchange linear and angular momenta, and energy upon collision. This allows a study of the sole effect of particle rotation upon fluid properties. Molecular dynamics simulations have been used to conduct extensive benchmark calculations of self-diffusion, shear and bulk viscosity, and thermal conductivity coefficients. As well, the validity of several kinetic theory equations have been examined at various levels of approximation as a function of density and translational-rotational coupling. In particular, expressions from Enskog theory using different numbers of basis sets in the representation of the distribution function were tested. Generally Enskog theory performs well at low density but deviates at larger densities, as expected. The dependence of these expressions upon translational-rotational coupling was also examined. Interestingly, even at low densities, the agreement with simulation results was sometimes not even qualitatively correct. Compared with smooth hard sphere behaviour, the transport coefficients can change significantly due to translational-rotational coupling and this effect becomes stronger the greater the coupling. Overall, the rough hard sphere fluid provides an excellent model for understanding the effects of translational-rotational coupling upon transport coefficients.  相似文献   

17.
The excess Helmholtz free energy functional for associating hard sphere fluid is formulated by using a modified fundamental measure theory [Y. X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)]. Within the framework of density functional theory, the thermodynamic properties including phase equilibria for both molecules and monomers, equilibrium plate-fluid interfacial tensions and isotherms of excess adsorption, average molecule density, average monomer density, and plate-fluid interfacial tension for four-site associating hard sphere fluids confined in slit pores are investigated. The phase equilibria inside the hard slit pores and attractive slit pores are determined according to the requirement that temperature, chemical potential, and grand potential in coexistence phases should be equal and the plate-fluid interfacial tensions at equilibrium states are predicted consequently. The influences of association energy, fluid-solid interaction, and pore width on phase equilibria and equilibrium plate-fluid interfacial tensions are discussed.  相似文献   

18.
基于对OZ 方程的渐近行为与Taylor级数展开的分析,提出了一个新的桥泛函,桥泛函被表达为间接相关函数的函数,Taylor级数展开的重整化导致了一个可调参数,通过将所提出的桥泛函与一个最近提出的密度泛函理论方法学,以及单个硬墙的sum 规则结合,可以确定可调参数.所提出的桥泛函能预言如下非均一流体的密度分布:硬球流体接近一个硬墙与在球形空隙内,Lennard-Jones 流体与缔合硬球流体在两个硬墙之内.理论预言与文献所报导的模拟数据符合很好.  相似文献   

19.
We present a study of the solid-fluid and solid-solid phase equilibrium for molecular models representative of chiral molecules and enantiomeric mixtures. The models consist of four hard sphere interaction sites of different diameters in a tetrahedral arrangement with the fifth hard sphere interaction site at the center of the tetrahedron. The volumetric properties and free energies of the pure enantiomers and binary mixtures were calculated in both fluid and solid phases using isobaric Monte Carlo simulations. The models exhibit essentially ideal solution behavior in the fluid phase with little chiral discrimination. In the solid phase the effects of chirality are much greater. Solid-fluid phase behavior involving the pure enantiomer solids and also racemic compounds was calculated. The calculations indicate that, depending on the relative sizes of the hard sphere interaction sites, packing effects alone can be sufficient to stabilize a racemic compound with respect to the pure enantiomer solids.  相似文献   

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