A new evolutionary crystallography algorithm predicts
the structure of crystals under a range of extreme pressure and
temperature conditions on the basis of the chemical composition
alone. One of these crystals would be a form of red-colored oxygen.
Predicting crystal structures is difficult even for simple solids,
partly because of the task of sorting among the astronomical number
of possible ways given atoms can compose a basic repeatable unit
cell.
Artem Oganov, a scientist at the Swiss Federal Institute of Technology (ETH)
in Zurich, in Switzerland, and Colin Glass, a
Ph.D. student, approach the problem by combining electronic structure
calculations and a specifically developed evolutionary algorithm. In
exploring the myriad atomic arrangements, they proceed in a
step-by-step, continual-optimization fashion that avoids
configurations less likely to succeed. This makes the algorithm very
efficient and allows the researchers to make certain specific
predictions.
One example is calcium carbonate (CaCO3) at very high
pressures. Oganov's team for the first time predicted two new
stable structures for this mineral. By now, both structures have
been confirmed in experiments by Japanese colleagues. Oganov and
Glass have also solved the structures crystalline oxygen at high
pressure.
Oxygen is unique from the chemical point of view. The
only magnetic molecular element known, under pressure it loses its
magnetism and turns red. The structure of red oxygen, which remained
unknown for a long time, seems to be finally solved and turns out to
be unique; that is, it does not manifest itself in any other
element. At even higher pressure oxygen is known to turn black in
color and become superconducting, which happens because of the
increased interactions between the O2 molecules. The ETH
researchers also predict a new stable phase of sulphur and several
new metastable forms of carbon.
Oganov and Glass,
Journal of Chemical Physics, 28 June 2006
Contact Artem Oganov, ETH Laboratory of Crystallography
+41-(0)44-632-37-52, a.oganov@mat.ethz.ch
Artem Oganov's Web page
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