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Reindexing: Difference between revisions
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The other use is in a final step that might have to be done in order to make the reduced data consistent with another existing dataset, or an atomic model. For some background, see [http://www.ccp4.ac.uk/dist/html/reindexing.html reindexing]. Unfortunately, even P1 crystals can have cells which may be transformed such that the indexing is different. An example is a triclinic cell with parameters a=58.5 b=73.1 c=83.6 alpha=80 beta=70 gamma=89 which gives similar cell parameters under the transformation REIDX=1 0 0 0 0 -1 0 0 1 0 -1 0. | The other use is in a final step that might have to be done in order to make the reduced data consistent with another existing dataset, or an atomic model. For some background, see [http://www.ccp4.ac.uk/dist/html/reindexing.html reindexing]. The classic description of this is that these are crystals where the Laue symmetry is of a lower order than the apparent crystal lattice symmetry. Unfortunately, however, even P1 crystals can have cells which may be transformed such that the indexing is different. An example is a triclinic cell with parameters a=58.5 b=73.1 c=83.6 alpha=80 beta=70 gamma=89 which gives similar cell parameters under the transformation REIDX=1 0 0 0 0 -1 0 0 1 0 -1 0. | ||
We should rather use the term "alternative indexing" for this mode of reindexing. | We should rather use the term "alternative indexing" for this mode of reindexing. | ||
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Attention: whenever there is a possibility of alternative indexing, there is also a chance that the crystal (and its data) may be twinned! In the example above, the twinning law is h, -k , h-l . A good tool to identify this situation is sfcheck. Whenever you see !!! WARNING !!! SOLUTION MAY NOT BE UNIQUE. in IDXREF.LP, you should be aware of this possible problem. | Attention: whenever there is a possibility of alternative indexing, there is also a chance that the crystal (and its data) may be twinned! In the example above, the twinning law is h, -k , h-l . A good tool to identify this situation is sfcheck. Whenever you see !!! WARNING !!! SOLUTION MAY NOT BE UNIQUE. in IDXREF.LP, you should be aware of this possible problem. | ||
FIXME: shortly discuss merohedral and non-merohedral twinning (example above) here. | |||
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