Thank you for all the quick reply. Here are the additional information about the crystal. The crystal was frozen and shot in synchrotron. The collection was 1degree/frame. The space group and unit cell are P21 and a=70 b=165 c=170 alpha=90 beta=90.1 gamma=90. I processed the data in P1 first (I did not see any abnormal changes during integration), and then merge them using P21 or P2221. P21 gives reasonable Rmerge of ~10% while P2221 has much higher Rmerge of ~30%. I reprocessed the data with mosflm using P1. And Pointless also suggested the space group of P21.
Zhiyi On 1/5/12, Jens Kaiser <[email protected]> wrote: > What are your cell constants and space group? It sounds to me you > misindexed and then artificially "twinned" your structure by > integrating/merging in too high of a symmetry. I've seen that happen for > primitive hexagonal which was actually C-centered monoclinic. > Also, in my experience this is more likely to happen with > denzo/scalepack as it refines every image and does postrefinement in > scalepack. XDS will decide for you on a symmetry after integration, and > in MOSFLM you should see earlier that something is wrong. > > HTH > > Jens > > > On Wed, 2012-01-04 at 21:42 +0800, Zhiyi Wei wrote: >> Dear all, >> >> I recently collected a dataset (~2000 frames) from a single crystal. >> If merge first 600 frames (sca1) or last 600 frames (sca2), Rmerge >> values from scalepack seem to be ok (~10%) though rejection ratios are >> high (~5%). But if I merge all frames together, Rmerge value goes up >> to ~20% and rejection is extremely high (~20%). Then, I checked sca1 >> and sca2 by xtriage in phenix. Surprisingly, the logfiles told me that >> sca1 is no twining while sca2 is very likely to be twinned. I never >> met this case before. So, I am wondering if it is possible from a >> non-twinned structure to a twinned structure just due to radiation >> damage. If the answer is yes, does it mean that I should not collect a >> large number of frames to amplify anomalous signals by using this >> crystal? >> >> Thanks a lot! >> >> Best, >> Zhiyi > > >
