| Years
ago, when Uzi Landman and his colleagues set out to
uncover some of the rules that govern why a non-reactive
metal like gold acts as a catalyst when it is in nanoclusters
only a few atoms in size, they didn't sit down in a
lab with the precious metal. Instead, they ran computer
simulations and discovered that gold is a very effective
catalyst when it is in clusters of eight to two dozen
atoms. They also found that electrical charging of gold
is crucial to its catalytic capabilities. Six years
later, the team has verified their earlier predictions
experimentally, and they stand ready to further explore
environmental effects on catalysis.
This practice of partnering
computer simulations with real-world experiments is
becoming more vital as scientists delve deeper into
realms where the actors are measured on the nanoscale,
Landman told a group of scientists Thursday, February
17 at the annual meeting of the American Association
for the Advancement of Science (AAAS).
"Small is different,"
said Landman, director of the Center for Computational
Materials Science and professor of physics at the
Georgia Institute of Technology. "We cannot use
the way physical systems behave on the large scale
to predict what will happen when we go to levels only
a few atoms in size. In this size regime, electrons
transport electricity in a different way, crystallites
have different mechanical properties and gold nanowires
have strength twenty times larger than a big bar of
gold, and inert metals may exhibit remarkable catalytic
activity. But we know the rules of physics, and we
can use them to create model environments in which
we can discover new phenomena through high-level computer-based
simulations."
Computers are constantly becoming
more powerful and capable of conducting more detailed
explorations at the same time scientists across the
globe are increasing their interest in the science
of the small. The intersection of these two trends,
said Landman, is allowing scientists to investigate
realms that are too small for today's technology to
explore experimentally.
It's not just a matter of making
faster calculations, he said. "Experimentally,
we can't always go down to the resolution we need
to see, explain and predict things, but with computer
simulations we can go to any resolution we need,"
said Landman. "Therefore, you can ask questions,
deeper questions, on how materials behave on the small
scale, even if you can't get to that fine resolution
experimentally."
This doesn't mean that experiments
aren't necessary, said Landman. "It's a supplementary
and complimentary approach. The pillars of scientific
methodology are composed now of experimentation, analytical
theory and computer simulation."
In addition to their work on
nanocatalysis, Landman and colleagues have used simulations
to explore other phenomena, such as the possibility
of producing and maintaining a stable flow of liquid
on the nanoscale. Their models predicted that it is
possible to produce liquid jets only six nanometers
wide. To date, in collaboration with Landman's theory
group, there are teams of engineers building nozzles
that can produce jets in the 100 nanometer range.
Within one year, said Landman, they expect to produce
"nanojets" in the 10 nanometer range.
"The
opportunity to make new discoveries in ways that weren't
possible before is an incredible gift and it has come
about only because we can now simulate environments
on the computer that are either not yet possible,
too expensive or too dangerous to do in the lab,"
said Landman. "We are now at a point in history
where the science of the small holds the promise of
producing a windfall of scientific discoveries. Computers
serve tools for discovery in this exciting adventure."
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