Theoretical and Computational Studies of Glasses and the Glass Transition

这是一个新的奖项，由多学科活动办公室（MPS）和材料研究、数学科学和高级科学计算部门联合资助。本文将对易碎玻璃形成液体的结构特性以及这种结构与弛豫机制的关系进行理论和计算的综合研究。在一些新技术中，玻璃已成为越来越重要的一类材料。它们具有重量轻、易于加工等优点，但会因蠕变、疲劳和脆化而退化。为了理解这些机制，有必要了解玻璃的结构和它们是如何放松的。目前，实验可以提供关于玻璃弛豫过程的信息，但对其结构或这种结构与弛豫机制的关系的信息并不多。相比之下，计算机模拟可以提供有关结构的信息，但只能在相对较短的时间和长度尺度上。而且，对玻璃的理论认识还处于比较粗糙的状态。在本研究中，将研究一系列模型，从玻璃形成液体的平均场模型开始，并通过各种近似方法进行，以包括非平均场效应。将使用几种并行计算机体系结构来扩展模拟系统的大小和时间尺度。模拟将基于有效的信息传递分子动力学程序，以及基于傅里叶加速算法和元胞自动机模型的更多推测方法。理论研究和计算机模拟的结果，结合波士顿大学和其他地方正在进行的实验室实验，将有助于理解在深度过冷液体和玻璃中实验观察到的弛豫与计算机模拟中看到的结构存在之间的关系。了解这种关系将使利用玻璃的结构来预测它们的时间演化成为可能。这项研究将与波士顿大学物理与电气系、计算机与系统工程系以及计算科学中心的同事合作完成。此外，克拉克大学和布兰代斯大学物理系、NIST计算材料中心和思维机器公司的同事也将参加。研究生也将参加由美国国家科学基金会赞助的波士顿大学计算科学中心研究生研究培训计划。计算机平台包括波士顿大学的38个处理器SGI Power Challenge阵列，一个工作站集群和几台CAM-8机器。克拉克大学和NIST Cray YMP的工作站集群也将被使用。这是一个新的奖项，由多学科活动办公室（MPS）和材料研究、数学科学和高级科学计算部门联合资助。该研究结合了美国国家科学基金会关于先进材料和加工以及高性能计算和通信的项目。本文将对易碎玻璃形成液体的结构特性以及这种结构与弛豫机制的关系进行理论和计算的综合研究。在一些新技术中，玻璃已成为越来越重要的一类材料。它们具有重量轻、易于加工等优点，但会因蠕变、疲劳和脆化而退化。为了理解这些机制，有必要了解玻璃的结构和它们是如何放松的。目前，实验可以提供关于玻璃弛豫过程的信息，但对其结构或这种结构与弛豫机制的关系的信息并不多。相比之下，计算机模拟可以提供有关结构的信息，但只能在相对较短的时间和长度尺度上。而且，对玻璃的理论认识还处于比较粗糙的状态。理论研究和计算机模拟的结果，结合波士顿大学和其他地方正在进行的实验室实验，将有助于理解在深度过冷液体和玻璃中实验观察到的弛豫与计算机模拟中看到的结构存在之间的关系。了解这种关系将使利用玻璃的结构来预测它们的时间演化成为可能。这项研究将与波士顿大学物理与电气系、计算机与系统工程系以及计算科学中心的同事合作完成。此外，克拉克大学和布兰代斯大学物理系、NIST计算材料中心和思维机器公司的同事也将参加。研究生也将参加由美国国家科学基金会赞助的波士顿大学计算科学中心研究生研究培训计划。计算机平台包括波士顿大学的38个处理器SGI Power Challenge阵列，一个工作站集群和几台CAM-8机器。克拉克大学和NIST Cray YMP的工作站集群也将被使用。* * *

9633385 Klein, Gould and Brower This is a new award which is funded jointly by the Office of Multidisciplinary Activities/MPS, and the Divisions of Materials Research, Mathematical Sciences and Advanced Scientific Computing. An integrated theoretical and computational investigation will be made of the structural properties of fragile glass-forming liquids and the relation of this structure to the mechanisms of relaxation. Glasses have become an increasingly important class of materials in several new technologies. They possess advantages such as light weight and ease of processing, but suffer from degradation through creep, fatigue, and embrittlement. To understand these mechanisms, it is necessary to understand the structure of glasses and how they relax. At present, experiments can provide information about relaxation processes in glasses, but do not yield much information about their structure or relation of this structure to the relaxation mechanisms. In contrast, computer simulations can provide information about structure, but only on relatively short time and length scales. Moreover, theoretical understanding of glasses is in a relatively crude state. In this research, a sequence of models will be studied beginning with a mean-field model of a glass-forming liquid and proceeding via various approximation methods to include non-mean-field effects. Several parallel computer architectures will be used to extend the size and the time scale of the systems simulated. The simulations will be based on an efficient message passing molecular dynamics program, and by more speculative methods based on Fourier acceleration algorithms and on cellular automata models. The results of the theoretical investigations and computer simulations, in conjunction with ongoing laboratory experiments at Boston University and other locations, will facilitate an understanding of the relation between the relaxation observed experimentally in deeply supercooled liqui ds and glasses and the existence of structures seen in computer simulations. Understanding of this relation will make it possible to use the structure of glasses to predict their temporal evolution. The research will be done in collaboration with colleagues at Boston University in the Departments of Physics and Electrical, Computer and Systems Engineering, and the Center for Computational Science. In addition, colleagues in the Physics Departments at Clark and Brandeis Universities, the Center for Computational Materials at NIST, and at Thinking Machines Corporation will participate. Graduate students will also participate through the NSF-sponsored Graduate Research Training Program at the Center for Computational Science at Boston University. Computer platforms include Boston University's 38-processor SGI Power Challenge array, a work station cluster and several CAM-8 machines. A workstation cluster at Clark University and the NIST Cray YMP will also be used. %%% This is a new award which is funded jointly by the Office of Multidisciplinary Activities/MPS, and the Divisions of Materials Research, Mathematical Sciences and Advanced Scientific Computing. The research combines aspects of NSF programs on Advanced Materials and Processing and on High Performance Computing and Communications. An integrated theoretical and computational investigation will be made of the structural properties of fragile glass-forming liquids and the relation of this structure to the mechanisms of relaxation. Glasses have become an increasingly important class of materials in several new technologies. They possess advantages such as light weight and ease of processing, but suffer from degradation through creep, fatigue, and embrittlement. To understand these mechanisms, it is necessary to understand the structure of glasses and how they relax. At present, experiments can provide information about relaxation processes in glasses, but do not yield much information about t heir structure or relation of this structure to the relaxation mechanisms. In contrast, computer simulations can provide information about structure, but only on relatively short time and length scales. Moreover, theoretical understanding of glasses is in a relatively crude state. The results of the theoretical investigations and computer simulations, in conjunction with ongoing laboratory experiments at Boston University and other locations, will facilitate an understanding of the relation between the relaxation observed experimentally in deeply supercooled liquids and glasses and the existence of structures seen in computer simulations. Understanding of this relation will make it possible to use the structure of glasses to predict their temporal evolution. The research will be done in collaboration with colleagues at Boston University in the Departments of Physics and Electrical, Computer and Systems Engineering, and the Center for Computational Science. In addition, colleagues in the Physics Departments at Clark and Brandeis Universities, the Center for Computational Materials at NIST, and at Thinking Machines Corporation will participate. Graduate students will also participate through the NSF-sponsored Graduate Research Training Program at the Center for Computational Science at Boston University. Computer platforms include Boston University's 38-processor SGI Power Challenge array, a work station cluster and several CAM-8 machines. A workstation cluster at Clark University and the NIST Cray YMP will also be used. ***