Chemist breaks 50-year-old barrier to better electron representation in molecular computations...
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Nov. 17, 2004 Press Contact: Steve Koppes
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Chemist breaks 50-year-old barrier to better electron representation
in molecular computations
Results apply to fields ranging from medicine to superconductivity
University of Chicago quantum chemist David Mazziotti has proposed a
new research tool that could help scientists more rapidly solve problems in
atmospheric chemistry, combustion, medicine and other areas of research
where the behavior of electrons plays a key role.
"We're in the pioneering stage so we're not going to go and treat all
of these problems right away," said Mazziotti, an Assistant Professor in
Chemistry. But with his new method, "we can do chemistry that cannot be done
otherwise," he said.
Mazziotti explains his method in the Friday, Nov. 19 issue of Physical
Review Letters. Further details will follow in early December in the Journal
of Chemical Physics.
The key to understanding whether or not a particular chemical reaction
will occur depends on a detailed statistical description of the electrons'
positions in the molecules involved. Until now, scientists have found it
necessary to attempt to represent the motion of all the electrons in the
molecule of interest-a daunting task requiring vast quantities of computer
power. "Just a single water molecule has 10 electrons," Mazziotti said.
But in the 1950s, researchers theorized that it should be possible to
accurately and more efficiently calculate the electronic properties of a
molecule using only a pair of electrons representing many-even hundreds-of
electrons in a molecular system. Mazziotti compares the feat to assembling a
set of architectural blueprints, which represent in two dimensions a
structure that can be built in three dimensions.
An architect follows certain rules to ensure that a builder can
translate a two-dimensional sketch into a three-dimensional structure. "In
the same way atoms and molecules consist of many electrons, but there is a
way to represent all of the electrons rigorously with only two electrons.
Certain rules have to be followed to ensure the two-electron ‘sketch' of the
molecule accurately represents all the electrons in the atom or molecule,"
Mazziotti's Physical Review Letters paper realizes a dream that
scientists have pursued for 50 years by introducing a set of instructions
for accurately and efficiently computing with a pair of electrons the many
electrons of the molecule. These instructions dramatically reduce the amount
of computer time and memory required to compute the electronic properties of
a molecule. Now Mazziotti can do some of the same calculations on his
desktop computer that previously required Japan's Earth Simulator, the
"David has really made a huge contribution in turning the dreams of 50
years ago into useful tools," said Bob Erdahl, a professor of mathematics at
Queens University in Kingston, Ontario. Erdahl said Mazziotti's Physical
Review Letters paper has applications to his own research in computing how
behavior at the subatomic level brings about macroscopic changes in
materials, such as the transition to the superconducting state.
"I'm certainly going to look very closely and try to incorporate
latest innovation into my work. I think we will very quickly be able to beat
other approaches in this area of solids and compute things that were out of
reach before," Erdahl said.
Erdahl is especially interested in determining why superconductivity
manifests itself only in two-dimensional layers rather than in
three-dimensional solids. "The computations are of course very difficult to
do. These methods that David is developing and that we're developing are
very helpful in attacking that problem."
While Erdahl works in mathematical physics, understanding the
electronic energies that atoms and molecules possess also affects almost
every area of chemistry. One such area, Mazziotti said, has broad
applications and includes the chemistry of free radicals-highly reactive
In atmospheric chemistry, free radicals are instrumental in reactions
leading to ozone depletion and the creation of greenhouse gases. Another
area is the combustion of hydrocarbon fuels, which creates a variety of
"A lot of people want to know which radicals are present in a given
combustion process and what reactions those were undergoing because that's
going to affect fuel efficiency," Mazziotti said.
A third area is medicine, because radical-type reactions are common in
the human body. Mazziotti noted that hydroxy urea therapy combats
sickle-cell anemia by forming a radical that triggers a cascade of
additional reactions. "There is a 40 percent reduction in mortality for
patients who receive hydroxy urea treatment for sickle cell," he said.
Despite the advances that Mazziotti and others have contributed to the
representation of electrons in atoms and molecules, further advances could
be in the offing. He said the field is experiencing a new wave of research.
"We're not done by any means."
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Last modified at 03:15 PM CST on Wednesday, November 17, 2004.