Chaotic Motion in Molecular Structures
J. Kieffer,* B. J. Reardon
University of Illinois; Los Alamos National Laboratory

By using concepts from chaos theory, such as Lyapunov exponents and Kolmogorov-Sinai entropies, we characterize the dynamic behavior of large molecular configurations generated by molecular dynamic simulations. From these measures one can derive conclusions about the thermodynamic stability of a structure, as well as estimate the magnitudes of atomic transport coefficients. The goal of this project is to develop formalisms that allow one to relate the topology of a structure to the inherent mobility of its constituents, and with this knowledge improve the design of electrolytes used in batteries, fuel cells, and sensors.

Computer Modeling of Microstructural Evolution in Porous Solids and Thin Films
J. W. Bullard*
University of Illinois

This research focuses on applying high-performance computing to simulate the dynamics of interface motion in complex microstructures and thin-film systems. The approach is based on both sharp interface and diffuse interface theories, and allows one to track interface motion readily. A number of thermodynamic driving forces for energy dissipation, as well as several kinetic mechanisms by which dissipation occurs, have been included. A diverse set of phenomena can be studied with this model, and it is currently being used to examine the growth and coalescence of thin-film islands, Ostwald ripening of precipitates, and the distribution of absorbed liquid in porous networks.

Electronic and Energetic Properties of Materials
D. D. Johnson*
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory and Oak Ridge National Laboratory)

Within a Green's function formalism, electronic density-functional theory (DFT) techniques are used to investigate disordered, partially ordered, and fully ordered phases of multicomponent alloy systems (such as substitutional alloys, ferroelectrics, high-Tc superconductors, battery and catalysis materials). The underlying electronic origin of various materials properties (electronic, magnetic, thermodynamic, elastic) are then determined. Additional schemes are being developed to investigate larger-scale phenomena, such as microstructure and kinetics, which are ultimately based on such DFT results, thus allowing a connection of length scales: micro- to macroscale.

Multiscale Simulation of Ceramic Materials
J. Kieffer,* J. W. Palko
National Institute of Standards and Technology

We develop multiscale simulation techniques for modeling the mechanical behavior of ceramic materials under nonequilibrium conditions and study phenomena such as phase transformation and catastrophic failure. The research encompasses the development of (1) improved models for the description of atomic interactions that mimic electronic configurations for all anticipated bonding types and nonbonding states, (2) acceleration algorithms to simulate processes governed by infrequent events, and (3) length-scale bridging strategies to effectively couple atomistic simulations with continuum mechanical computations. Accurate simulation of the mechanical behavior in real materials is achieved by atomistically resolving critical parts of microstructures, such as crack tips or grain boundaries.

Simulation of Crystallization of Inorganic Compounds
J. Kieffer,* R. B. Rao
University of Illinois; National Science Foundation, DMR 93-15779 REU

The crystallization from supercooled melts of inorganic compounds in computer simulations was deemed impossible because of the high activation energies for atomic migration and the ensuing large time scales necessary for such simulations. Recently we have been successful in crystallizing various alkali-halides and their mixtures, from highly supercooled melts, using molecular dynamic simulations. With this method, we now study nucleation processes, the various defects that develop upon crystal growth, and the relationship between crystallization behavior and the thermodynamic phase diagrams.

Structure, Topology, and Properties of Metallic Nanoclusters
D. D. Johnson*
National Science Foundation, DMR 99-76550 (In cooperation with the Materials Research Laboratory)

Metallic and bi-metallic nanoclusters play an important role in fuel cell and catalysis applications. We plan joint DPT-based and empirical-based simulations to predict structure, topology and electronic properties of such clusters, as well as to explain on-going experiments in these materials by Nuzzo et al., and their apparent self-organization.

Theoretical Sociophysics
R. J. Gaylord*
University of Illinois

Agent-based models of social behavior are being developed. The spatial metric used in describing physical systems is supplemented and/or replaced by the use of a social metric. Moreover, the agents are heterogeneous in their individual characteristics and in their social connections to other agents, both of which may vary over time. The models are tested using computer simulation studies.