CRYSTAL STRUCTURE PREDICTION:
A TOOL FOR CRYSTAL STRUCTURE DETERMINATION
Detlef W. M.
Hofmann
Institute for Algorithms and Scientific Computing, German
National Research Center for Information Technology (GMD-SCAI),
Schloß Birlinghoven, 53754 Sankt Augustin, Germany, E-mail: detlef.hofmann@gmd.de.
Keywords: statistical potentials, discrete molecular
modeling, crystal structure prediction
Organic molecule crystals are becoming more and more important
in applications like piezoelectricity, ferroelectricity, drugs
and pigments. The properties like color or bioavailibility depend
on the molecule and on the crystal structure. For
characterization and understanding it is necessary to determine
the crystal structure. If large single crystals are available the
structure can be easy determined by direct methods, but in some
cases only the powder diffraction is avaliable. This is often the
case for pigments and steroids, which are difficult to
crystallize. To determine the crystal structure from the
diffraction one needs good trial structures. For this purpose we
have developed the program FlexCryst [1,2]
differing mainly in three features from other approaches
(simulated annealing, Monte Carlo etc.). First, we analyze just
one molecule for proper symmetry operations building up the
crystal; second, the program works in a discrete space; and
finally the scoring function (energy function) is derived
statistically from known crystal structures and tabulated. Our
program computes a list of crystal structures weighted according
to our scoring function.
The first ten structures were optimized by a force field and
refined with the Rietveld procedure. The procedure was applied to
all structures of space group P1 contained in the Cambridge
structure database. Structures, which were not a minimum in the
force field were screened off. For the remaining crystals we did
'solve' the structure for 87 cases of 89 examples. Only two
structures were not found. The overall calculation time was five
minutes per crystal structure.
References
This is a structure generated by FlexCryst. Please click in and
play around with the crystal!