Diana Farkas

This project involves a basic study of the structure of various defects in materials at a molecular atomistic level. The project uses descriptions of the interactions between the various atoms that are based on both experimental data as well as first principle quantum mechanical calculations. The technique we presently use for the interatomic forces is the embedded atom method (EAM) and a modified version of the method that we have developed. Once this description is obtained the equilibrium atomic configuration around any defect can be calculated through various energy minimization schemes, molecular dynamics or Montecarlo techniques. The detailed information on the atomistic configuration of the defective region is then linked to the properties in the material that are controlled by such defects. The Atomistic Simulation Laboratory has been involved in atomsitic computer simulation of materials behavior for more than 10 years now. In recent years the increased speed of available computing facilities have allowed us to undertake large scale massive simulations. It is now possible to conduct simulations involving millions of atoms and study the structures of defective solids and their relation with material properties.

These large scale simulations pose new challenges in the ways in which the results can be visualized and analyzed. Conventional two dimensional scientific visualization packages usually can not handle the large number of atoms involved in these massive simulations. Furthermore, the new computer architectures and increasing speeds allow the study of defects that are truly three dimensional in nature. This means that the results have to be visualized necessarily in three dimensions. An example of this type of simulation is the work on the study of cracks in intermetallic materials that is currently under way in the Laboratory. This work is now possible in three dimensions using realistic crystal structures for the materials considered and also realistic descriptions of the energetic interaction among the atoms. Molecular statics and molecular dynamics studies of crack behavior require complex visualization schemes in order to translate the three dimensional structure into various two dimensional plotting schemes. CAVE visualization will allow this research to take a qualitative step forward since the structure of the crack and surrounding area can be seen in a direct way.

During a recent visit to NCSA's CAVE a sample simulation was already visualized in the CAVE, using applications already in place. These preliminary results indicate that the benefits of CAVE visualization on the fracture mechanics studies at an atomistic level are indeed going to lead to qualitatively new possibilities. Similar benefits are expected in the studies of various other defects underway in our laboratory such as the structure of stepped surfaces, grain boundaries and interfaces in various materials. Our current work is sponsored by NSF and ONR representing a large effort in the area with a group of two postdoctoral research fellows and six graduate students.