Dynamics of Equilibrium Liquids, Supercooled Liquids, and Glasses

斯坦福大学的Hans Andersen在理论和计算化学计划的支持下，继续发展理论方法，在分子水平上计算液体、过冷液体和玻璃的动力学性质。基本策略是使用形式上精确的理论来创建液体的近似动力学理论，然后进行分子动力学计算机模拟来测试这些近似的准确性。通过这项研究，将开发出能够描述低温液体中发生的重要物理过程的实用和准确的近似。这个项目的具体目标包括：(1)了解和定量描述当液体材料被冷却时，分子在其邻居形成的“笼子”中长时间被困时，分子动力学中发生的变化；(2)了解在过冷液体中发生的结构变化如何影响动力学；(3)了解发生的各种弛豫过程及其之间的关系；以及(4)了解在极低温度下导致玻璃转变形成的非常缓慢的弛豫过程。玻璃是技术上重要的材料，由各种成分制成，既有有机的，也有无机的，既有低分子物质，也有聚合物。例子包括普通材料，如窗户玻璃和食品容器，以及先进材料，如用于电信的光纤、光电子和固体电解质。这些材料的性能取决于它们是如何制造的，使用的方法通常包括制备高温液体，然后进行各种冷却和加工步骤。目前，最佳性能材料的创建在很大程度上受到经验观察的指导。通过增加对这些材料及其相应液体动力学的了解，合理加工程序的设计有望得到加强，这些研究工作将出现。

Hans Andersen of Stanford University is supported by the Theoretical and Computational Chemistry Program to continue development of theoretical methods to calculate dynamical properties of liquids, supercooled liquids, and glasses at the molecular level. The basic strategy is to use a formally exact theory to create approximate kinetic theories of liquids, and then perform molecular dynamics computer simulations to test the accuracy of these approximations. Practical and accurate approximations capable of describing important physical processes that take place in low temperature liquids will be developed through this research. The specific objectives of this project include: (1) understanding and describing quantitatively the change that occurs in the dynamics of molecules as a liquid material is cooled and molecules become trapped for an extended period of time in a "cage" formed by its neighbors, (2) developing an understanding of how structural changes that take place in supercooled liquids can affect the dynamics, (3) understanding the variety of relaxation processes that take place and the relationships among them, and ultimately (4) understanding the very slow relaxation processes at very low temperature that lead to the formation of a glass at the glass transition. Glasses are technologically important materials made from a variety of components, both organic and inorganic, both low molecular weights substances and polymers. Examples include ordinary materials such as window glass and food containers, as well as advanced materials such as fiber optics for telecommunications, optical electronics, and solid electrolytes. The properties of these materials depend on how they are made, using methods that usually involves preparation of a high temperature liquids followed by various cooling and processing steps. The creation of optimal performance materials is currently guided largely by empirical observations. Design of rational processing procedures is expected to be enhanced by the increased understanding of dynamics of these materials and their corresponding liquids that will emerge from this research effort.