A Computer Simulation Study Of The Microcosmic Structure Of Liquid State And Amorphous State

The microcosmic structure of the condensed state has always been an important topic which physicists, biologists, chemists and material scientists explore teeth and nail. To induce the law of order from the orderless structure of the condensed state, quantificational description is an absolutely necessary tache. However, because of the well-known difficulty, such quantificational description was not possible until the computer simulation came out. With the development of computer science and computational science, to open out the arcanum of the microcosmic structure by computer simulation has become the hotpot and the leading field of the research on the condensed state. Taking the instantaneous configurations of the system obtained by the computer simulation with molecular dynamics method as source data, this thesis conducts the quantificational description of the system's microcosmic structure by means of several geometrical methods, and it aims at obtaining a clear physical model of the microcosmic structure of the condensed state.Because of simple conception and clear geometric pattern, V-D theory has been getting more and more recognition. V-D network contains powerful information of the system, and it can provide basic geometrical data for the research of the system's microcosmic structure. This thesis utilizes the extended V-D geometrical model, adopts the revised method of constructing and computing the Voronoi polyhedron and the tracing method based on Voronoi S-network, to conduct much calculation and statistical analysis for the geometric parameters from the aspects of the measurement characteristic and shape characteristic of the microcosmic structure in the melting process of alkali metals halide which is represented by LiCl crystal, and some plentiful and substantial results have been obtained.The main contributions of this thesis include1. Systematically summarizing the V-D method for different systems of discrete point set, spheroid and non-spherical convex body, and applying an improved method to studying the melting salt of alkali metals halide and the solution of the melting salt;2. Revising the successive cutting method of constructing and computing the Voronoi polyhedron to make it applicable to the occasions of different radii particles, multiplicate particles and sub-Voronoi polyhedron; developing the new research method of replacing the bond-angle by the Delaunay simplex(DS) face angle for the problem of scale superposition of the bond-angle parameter in the analysis of the Voronoi polyhedron;3. In allusion to the particularity of structure of melting salt, developing the cubic degree as a new parameter for measuring DS and its computer realization, developing the new idea of crystal surface DS and crystal lattice DS for ion systems, and integrating the scale analysis of volume, area, sphericity degree, tetrahedral coefficient of the simplex to develop the melting theory based on the parameter analysis of simplex and make it more general;4. For ion systems, developing the new concepts of sub-DS network, centered sub-DS and centerless sub-DS and the computer realization method of these sub-DS; based on these concepts, developing the new research methods of intermediate range structure by using the sub-DS network based on classifying positive ion and negative ion and the sub-DS network based on classifying positive ion and negative ion in accordance with the four particles group constituting the sub-DS; for the particularity of Voronoi network, developing the research method of mixed multi-coloration;5. Since the existence and distribution of the microcosmic hole are closely related to the system properties, by using the V-D method, we revise and complement the embedding technique to make it find the microcosmic holes of the system more effectively, in addition, we discuss the structure of microcosmic holes of the system accordingly.Though there are many research results overseas on liquid theory, most of these studies take Lennard-Jones(L-J) model liquids as objects. Research on melting salt and the solution of melting salt using V-D theory is rare. The research method of this thesis chooses melting salt and the solution of melting salt as the implementary objects. These choices are not only because of the application value of melting salt system in the aspects of metallurgy and new energy sources (fuel batteries of melting salt, nuclear reactor of melting salt, solar dynamoelectric heat storage medium, etc.), but also due to that melting salt consists of both negative ion and positive ion, research on them using V-D theory can obtain much more structure information than the monoatomic molecule liquid, and thus the research of this thesis contributes to the structure theory of general liquid state. In addition, the computer simulation of melting salt forming non-crystal solid through quenching can be easily realized by means of molecular dynamic method, so the research results of the melting salt structure in this thesis may enlighten the research on non-crystal ion solid.This thesis is organized as follows: Chapter 1 presents the introduction; Chapter 2 describes the geometrical knowledge of V-D method and the realization of V-D method on the computer; Chapter 3 presents the parameter analysis for the Voronoi field of local structure in LiCl melting process; Chapter 4 presents parameter analysis for the Delaunay S-simplex of local structure in LiCl melting process; Chapter 5 explores the intermediate range structure of alkali metals halide; Chapter 6 introduces the analysis method of microscopic hole; Chapter 7 summarizes the thesis.