Applying Science

Jeff Hammond

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“The chemistry part of computational chemistry really does come last,” Hammond says.  “Half the time you’re thinking about theoretical physics, another 45 percent of the time is spent getting the code to work correctly, and only then do you spend about five percent of the time actually thinking about chemicals.”

From a simulation of oxygen dichloride solvated in carbon tetrachloride. Click image for larger version and more information

When Hammond and others on the NWChem team did get to the chemistry, the results were impressive. They demonstrated the new code’s ability to simulate the molecular properties of oxygen dichloride and carbon tetrachloride in solution. This is a crucial capability, because most pollutants and almost all biological molecules exist in solution, usually water.

“At the end of the day we’re getting closer to giving biologists and nuclear scientists the ability to model things that are dangerous to study firsthand, or simply impossible to do so — for example, the interaction of uranium and other molecules in groundwater,” Hammond says.

The researchers also modeled the spectra of a group of complex organic molecules that includes polyaromatic hydrocarbons, or PAHs.  They ran the largest calculations of this kind ever performed and were able to determine the spectroscopic properties of these molecules at a level of accuracy not previously possible.

“The massively parallel codes developed by Jeff enable the full integration of the coupled cluster codes with NWChem’s existing molecular dynamics module, and this is truly cutting-edge,” PNNL’s DeJong says.  “For the first time ever, this merger will enable us to model the properties of the molecule with the full inclusion of surrounding environment. We believe that this will have a profound effect on the interplay between theory and experiment.”

Hammond’s contributions to NWChem will be available to the computational chemistry community in the next release of the software, expected in late 2007.  The research resulted in at least four papers, with more to come as an ongoing collaboration expands in scope.

Back at the University of Chicago to continue his thesis work, Hammond says his time at PNNL and driving past Hanford “profoundly changed the way I’m going to do things in the future.”

“By using existing methods and software, rather than starting from scratch, I can spend less time deriving equations and debugging code, and more time studying important chemical problems,” he says.

In addition to his mostly–theoretical thesis research, Hammond also wants to talk to a University of Chicago spectroscopist about PAHs in space. These organic molecules produced by dying stars are plentiful in interstellar space, and are thought to be a key source of organic material for the origins of life.  Hammond’s work with NWChem could help astrobiologists identify PAHs in interstellar space — one more application of his science that could help all of us see the really big picture.

 

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