Simulations at the Nanoscale

William A. Goddard III and Tahir Cagin

.
Materials and Process Simulation Center (139-74)
Division of Chemistry and Chemical Engineering
California Institute of Technology, Pasadena, CA 91125

A critical challenge in developing commercial nanoscale technology is the development of reliable simulation tools to guide the design, synthesis, monitoring, and testing of the nanoscale systems. Thus it is essential to build fast computational software that reliably predicts the chemistry and physics (structures and properties) as a function of conditions (temperature, pressure, concentrations) and time. Since we wish to synthesize new structures with new properties, it is essential that the software be capable of de novo or first principles predictions, prior to synthesis and characterization. Such software must also predict spectroscopic signatures (IR, Raman, UV, NMR) and properties (density, color, surface tension) that enable experimentalists to gauge the progress in the reactions and processes.

The critical difficulty facing the theory point is that such systems are too large for standard atomistic approaches (a cube of polyethylene 100 nm on a side contains about 64 million atoms). This requires a hierarchy of investigative tools connecting from quantum mechanics, through molecular dynamics, through a mesoscale level of description much coarser than atomic to the continuum or macroscale level (where the systems is described with a finite element mesh). The relationships between various scales in the hierarchy of modeling approaches are illustrated in the Figure. Great progress in developing these tools is being made at various laboratories. We will outline some of the advances and their implications.

As will be presented at this conference, much progress is being made in synthesizing and assembling nanoscale structures with interesting and unique properties. We will suggest some new strategies based on using catalysts to synthesize unique structures not easily synthesized using traditional techniques. These systems will be simulated using de novo atomistic and mesoscale simulation techniques to generate the structures and properties of some nanoscale novel devices. In addition, we will propose and test with atomistic simulations some nanoscale catalysts that might serve as useful reactors and energy sources for nanoscale systems.