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. ***
