I have three component twin of incommensurately modulated structure. How can I integrate it with CrysAlisPro? There is some information about it in manual but it isn't understandable without experience.
Many thanks for everybody for help and reply.
Hello, Pavel
You are asking a very tricky question and it sounds not to much promising to get something out of this.
I would first start with detwinning without introducing incommensurate model at first. I think it may be possible to suppress satellite peaks (if they somehow hinder to find twinning model) using a filter for intensity in the Ewald viewer. If detwinning is not successful (many reflections overlap), I think this would be useless to introduse incommensurate model. By the way, incommensurate structure should show temperature dependence, and at some given temperature it becomes commensurate (what twin will never do). So, it is a good reason to prove first the incomm. effect really takes place. Sometimes it is imaginary, and diffraction pattern can be described entirely with twinning components only. One example that I know is in SI in this paper
http://onlinelibrary.wiley.com/doi/10.1002/anie.201411451/full
I would first to try getting an acceptable model for the average structure to evaluate the chance to improve it with incommensurate effects. if its too bad, probably the task is too complicated even for Crysalis...
But if you managed to succassfully detwin the structure, try to introduce incommensurate vectors in the Ewald viewer. I would thoroughly analyse if it is again worth troubles, and many individual (not overlapped) reflections are present. If most of them overlap, there is no chance to integrate them one from another. The programm does it on the basis of profil analysis and if there is not enough data for good profiles, the deconvolution will be wrong.
Suppose, you successfully did this, then you need to integrate the data. In data reduction options swich off the box 'follow significant sample wobbling' (otherwise the reflections for different twin components can be mixed up saying nothing of the satellites...) and in Proffit special pairs menu check the box 'hkl check in 3D peak analysis'. Of course do not save memory and make the best possible background substruction.
Good luck with this, and if you do not find a good solution, try to ask the same question in the forum at Rigaku website. You can even contact Dr Matthias Meyer, the author of Crysalis and ask him porsonally.
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