【作者】 朱素华；

【导师】 郭进； 徐桦；

【作者基本信息】 广西大学 ， 理论物理， 2004， 硕士

【摘要】 熔融碱金属卤化物因为技术上的和基本理论上的双重原因而引起人们广泛的兴趣。但由于熔盐温度高、腐蚀严重，一些常规的物理化学方法难以准确地描述其结构和性质。随着计算技术的提高和计算机的发展，用计算机模拟方法研究熔盐的结构和性质越来越受到重视。作为计算机模拟的重要方法之一的分子动力学(MD)模拟不但能够在微观层次上理解和解释实验数据，而且在用实验手段无法研究或者实验研究花费昂贵的情况下更显示出它的优势。MD模拟已经成为研究熔盐和熔盐溶液理论的一种重要工具。模拟的结果对于理解其粒子间相互作用和结构具有重要意义。 上个世纪70、80年代，用MD方法对纯碱卤化物熔融盐作了很全面的研究，模拟获得的原子水平微观细节和统计热力学性质很好的解释了实验，验证了这部分理论的正确性。对二元碱卤化物熔盐系统混合效应的MD模拟，主要集中在共阴离子系，得到的结果也与实验和理论符合得较好。对共阳离子熔盐系统的MD研究甚少，而且模拟的结果与现有的实验结果差距很大；另外，实验结果和理论分析结果也有矛盾。至今，共阳离子系统混合效应还是一个疑难问题。 本论文的主要工作是从势函数入手，提出合理修正，然后用这种势函数对三种典型的二元共阳离子熔融碱卤混合物KF-KCl、NaF-NaCl和KF-Kl进行了MD模拟，模拟表明上述疑难问题定性上可以解决，定量上基本符合。本论文主要内容如下：广西大学硕士学位论文在第一章中，回顾了分子动力学方法和碱金属卤化物的MD模拟的发展和现状。在第二章中，分析了模拟使用的MO方法的相关内容，包括概念、假设、算法技巧、数据分析方法、程序结构及执行等。 由于势函数对M。模拟至关重要，所以，在第三章中，对碱卤化物Fumi一Tosi势及其常用势参数进行了较为详细的分析。分析表明，Ma，er的Van der waa 15系数C。，D。偏小和短程排斥势硬度参数有待改进。引入了一组新的Van der Waa 15系数。在此基础之上，对排斥参数进行了计算。计算得到的基本半径与Fumi一Tosi的一致，短程排斥势硬度参数发生了变化。同时讨论了碱金属卤化物混合系势参数的取值方法。 在第四章中，用MO方法分别对熔融KF一KCI、NaF一NaC}和KF一Kl在整个浓度范围1273K的混合效应进行了研究。模拟采用了两套参数。 对混杂烩的计算表明:采用Tosi一Fumi和Mayer的参数，混杂烩只在大离子端与K!ePpa的实验一致，采用Tosi一Fumi和Ja in etal的参数，混杂烩在两端都与实验一致。分析表明:(1)系统中库仑力和非库仑力对混杂焙的贡献是同等重要的，这与K}即Pa对包含氟化物的二元碱卤混合物的实验结果分析一致;(2)前者低估了非库仑力对混杂恰的贡献，这与尺ee和Holt的理论分析一致，与本文第三章的讨论一致。(3)非库仑能和库仑能的非线性变化对二元混合物的混杂过剩烩的贡献不能归结为库仑能对混杂烩的贡献一定是负的或非库仑能的贡献是正的这样的结论。分析了模拟结果与实验结果之间在广一西大学硕几_卜学位论文定量上存在误差的原因。 对偏径向分布函数研究表明:(1)两套参数对应的各对径向分布函数的第一主峰高度和位置的随摩尔分数变化的趋势基本一致，即随着氟离子摩尔浓度的增加，溶液中粒子集团化更高。(2)极化的增加也使粒子集团化程度变高。值得一提的是运用Tosi一Fumi和Ja ineta}的参数得到g、_厂的和g、_冲·)的主峰上出现了一个侧峰，这是从未观察到的。更多还原

【Abstract】 Fused alkali halide is of technological and theoretical importance and as such has attracted considerable interest. But due to its high temperature and severe cauterization, its structure and properties are difficult to accurately describe through some conventional physical or chemical methods. As calculating and computer techniques are developing fast, people shift more and more attention to research into the structure and properties of molten salt liquor by computer simulations. Molecular dynamics (MD) method, an important way of computer simulations, can not only help apprehend and explain the experimental data on a micro level, but also excel when such a simulation can’t be done laboratorially or when the laboratorial cost is too high. MD has become a vital implement for the research on the molten salt and its liquor theory. The simulation results are very important for understanding the interaction and structure between the particles in the molten salt and its liquor.In 1970’s and 1980’s, comprehensive investigation has been done on molten pure alkali halides using MD. Micro details on an atomic level and statistical thermodynamics properties obtained from MD have given a valuable insight on experimental results and validated the theories about pure alkali halide melts. MD simulations on the mixing effects of binary molten alkali halides are mainly concentrated on common-anion systems and there is satisfactory coincident with experimental and theoretical results. But there is very little investigation on common-cation systems, and that there are many discrepancies between experimental and simulation results. Furthermore, the experimental observation is inconsistent with that of theoretic analysis. As yet, the mixing effect of commom-cation molten alkali halides is still in doubt.The main work of this dissertation is to put forward the sound modification through potential functions. By using the potential functions, Md simulation of three binary common-cation molten alkali halides KF-KCl, NaF-NaCl and KF-KI is done. The simulation has revealed that the problem can be solved qualitatively, and the quantification can be accorded. Contents of this thesis are following:In Chapter 1, the development and the status quo of molecular dynamics method and alkali halide are reviewed.In Chapter 2, aspects of MD methods to be adopted in the simulation,including the concepts, hypothesis, arithmetic techniques, data analysis methods, steps and procedures are analyzed.In chapter 3, the Fumi-Tosi potential function of alkali halide and its general potential parameters are analyzed in detail for their vital roles in MD which indicates the Mayer’s Van der Waals coefficient Cij,Dij is small and thehardness parameter of short range repulsive potential needs revised. We introduced a new series of Van der Waals coefficient and had the repulsive parameter recalculated. The basic radius which we got is consistent with Fumi-Tosi’s while the short range repulsive potential hardeness parameter changed. Meanwhile, we discussed methods of achieving mixing alkali halide’s potential parameter.In chapter 4, the mixing effects in molten KF-KCK NaF-NaCl and KF-KI mixtures are studied at 1273K over the full concentration range by MD simulation, respectively. Two series parameters are adopted in the simulation.Calculations of the excess mixing enthalpy reveal: if by Tosi-Fumi’s and Mayer’s parameters, the excess mixing enthalpy is consistent with the Kleppa’s experiment at the big ion end; if by Tosi-Fumi’s and Jain et al’s parameters, the excess mixing enthalpy accords with the Kleppa’s experiment at both ends. Three conclusion may be drawn from these preliminary results: (1) the contribution of coulomb force and non-coulomb force to the excess mixingenthalpy are equivalent, which is consistent with Kleppa’s experiments on binary alkali halide containing fluoride; (2) the former underestimates non-coulomb force’s contribution to the enthalpy mixture, which accords with Ree and Holt’s theoretical analysis and also with our disc更多还原