A team of scientists from Syracuse University uses periodic quantum chemical calculations to figure the limits of molecular quantum theory in describing molecular crystal properties.

by Katherine A. Caponi

Chemists make many compounds that can be prepared in crystal form, three-dimensional solids arranged in a repeating pattern. The physical and chemical properties of those compounds, or crystalline solids, depend on two factors: the type of molecules that they are composed of and the arrangement of those molecules.

Unfortunately, there is no accurate method for predicting the arrangement that those molecules will take, which currently makes it impossible for scientists to design crystalline solids with useful traits. This difficulty must be overcome to make synthetic organic chemistry a practical tool for materials engineering.

One much-discussed example of this problem is a type of crystal that converts laser light from one color to another. For the crystalline solid to have that ability, the arrangement of molecules within the smallest repeating unit must be asymmetrical. However, there are many possible ways the molecules may arrange themselves when forming crystals. Scientists are trying to find a way to predict what conditions must be present in order for a particular arrangement to occur so that they can produce crystal with that quality in the lab.

Bruce Hudson and a team of scientists from Syracuse University are trying to break down such barriers. Because computational methods for studying crystals have only recently become widely available, chemists have not previously studied them with these methods. The Syracuse team uses NCSA's IBM p690 and now-retired SGI Origin2000 and other supercomputers to evaluate the accuracy of solid-state quantum chemical theory in comparison to experimental methods that investigate crystals and the quantum chemical methods commonly employed to examine isolated molecules.

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Access Online | Posted 6-15-2004

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