Computer Simulations On Atomic Packing Pattern And Its Evolution During Condensation

The experimental and computer simulation researches on the microstructure of liquid and metallic glasses win a wide approval from colleagues both home and abroad. This issue focuses on the atomic packing patterns in a systematic way based upon the above researches of the lab. The knowledge of allotropes induced such a concept of that atomic packing patterns dominate the microstructures of materials and that the differences in microstructures often affect significantly the physical and chemical properties of materials. The discovery of fullerene C60 and carbon nanotubes provoked the attention to atomic packing. However the studies on the atomic packing in the process of condensation were fairly inadequate. This situation is mainly due to the backward research techniques and research tools at that time. One of the reasons locates on the difficulty of experimental studies at high temperatures, and the other is the limited theoretical development of liquid materials.With the development of science and technology, it is now possible to study the structure of liquids in a vast variety of methods, and that sets a good foundation to support each other and corroborate each other. Direct measurement, inference from physical properties and theoretical calculation, these three types of research approach has established a cross-reference to the experience and theory. Theoretical calculations can be a good comparison to experimental tests and they are at the same time helpful to obtain information of the microstructure, which is hard to reach from a direct measurement. By this way, people can find out the internal mechanism of the process of condensation.Based on a fitting method using Monte Carlo random walk, this dissertation set up an effective potential model of Ag-Rh noble metal alloy. It was established by pair distribution functions, which was obtained from the Fourier transform of structure factors. Structure factors can be deduced out of experimental data coming from X-ray diffraction. This interaction potential function can effectively reflect the potential field model of particular materials. It hence laid down a foundation for further study of atomic packing of binary liquid melts and amorphous alloys.Atomic packing patterns of icosahedron and other polyhedra were investigated using reverse Monte Carlo method to reveal their influence on the forming of metallic glasses and their evolution features in the process of condensation from melts to metallic glasses. These clusters could hinder the nucleation of melts. The development of icosahedra clusters increases the glass forming ability of melts. It provides a richer understanding of metallic glasses and microstructure condition for the preparation of metallic glass.Forward molecular dynamics simulation method was adopted to study non-metallic nanowires. We found that atoms of nanowires in carbon nanotubes can exist in different packing patterns, which may have a significant impact on physical properties of materials. Among these packing patterns, spiral packing is important in the growth of materials evolution. The electrical properties of straight packing and spiral packing were discussed, which supplies some theoretical materials for the design and application of nanodevices.Upon investigating the condensation of phosphorus and silicon solidifying on surface of carbon nanotubes, we discover that, in heterogeneous nucleation process, heterogeneous nuclei have a great impact on the packing patterns of melt atoms. The condensed structures have a close correlation with that of the stronger nuclei. Under the driving of carbon nanotube, phosphorus and silicon atoms evolved into concentric cylinder structures around the carbon nanotube, forming some tree-ring like pipes. The silicon or phosphorus atoms tend to develop isomorphic structures identical to carbon nanotube as the stronger impurity.This dissertation has get along with the development of atomic packing pattern in the process of condensation. Some related know-how of condensed materials were carefully studied, some effective computation skills were probed, some interesting phenomena of physics and materials were discovered, and some heuristic results and conclusions were attained. That solidified also my effort to the application of amorphous materials and nanoscale devices and marked a new starting point for further research and application of this subject.