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Published online 5 December 2007 | Nature 450, 771 (2007) | doi:10.1038/450771a
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Model predicts structure of crystals
Software solves long-standing chemical frustration.
“One of the continuing scandals in the physical sciences is that it remains impossible to predict the structure of even the simplest crystalline solids from their chemical composition.” So wrote the chemist and former Nature editor John Maddox in 1988 (see Nature 335, 201.
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This is undoubtedly a remarkable achievement. There are but two points I would like to make. X-ray crystallography has changed dramatically not only over the last 100 years but even the last 10 years. The experimental determination of crystals structures of molecules like those used in the round-robin for crystal structure prediction can now be achieved within hours, no longer does it take weeks or even months. Crystallographers still need of course crystals, but the required size, in terms of volume, has shrunk by at least a factor of one hundred. I feel it should also be mentioned, that predicting correctly a stable crystal structure of a small organic molecule has to be followed by actually growing crystals of that polymorph, even if these are polycrystalline powders before one can claim a new crystal form. At least for the present time crystallisation remains a trial-and-error process. (Christian W Lehmann, Muelheim, Germany)
I feel I should make some comments, as the organiser of the latest crystal structure prediction blind test. The Avant-Garde/Bradford group should be congratulated for the four-out-of four success. However, I want to emphasize that it was not just this one method, which employs periodic electronic structure calculations, that performed well in this year's exercise. There was also increased success over past blind tests from several research groups who used sophisticated atomistic models (treating the molecules quantum mechanically, but using model potentials for intermolecular interactions). So we should not read the results as meaning that one solution to crystal structure prediction has emerged, rather that several quite different approaches have demonstrated important progress. The molecules included in the blind test are small and, in the context of pharmaceutical applications, the impact that various methods could make will depend on how they scale to larger, more flexible molecules. In extending to larger systems, the computational cost will be an issue and this is significantly higher for periodic quantum mechanical calculations than for atomistic approaches. This year's blind test results are exciting and I look forward to seeing how things develop over the coming years. I encourage anyone interested to keep an eye out for the full publication of the blind test results that is in preparation. As in previous years (Acta Cryst 2005, B61, p.511; Acta Cryst 2002, B58, p.647; Acta Cryst 2000, B56, p.697), the paper will provide details of the methods and results from all of the research groups who took part in the exercise. (Graeme M. Day, University of Cambridge)