Re: [ccp4bb] Twinning/Spacegroup Woes

Hi Rhys, We had a similar problem where initial data processing suggested P6522 space group but the content of the crystal was too large to fit in the unit cell (one well known symptom for twining). I reprocessed the data in P6, P312, P321 and finally the solution was obtained in P6 (P65). Howeve

Re: [ccp4bb] Twinning/Spacegroup Woes

Hi, I mentioned that R factors went down because they went down dramatically, from 33/36% to 22/24% (which shows that application of twinning does the right job even if such R-factors cannot be compared), and I have ‘seen’ such dramatic change for one of my small molecule refinements in old day

Re: [ccp4bb] Twinning/Spacegroup Woes

Hi, since several people mentioned R factors in this conversation I thought I remind that R-factors are not comparable between refinements using twinning and not. For example, R-factor decrease after switching to twin refinement doesn't mean much; you can't use R factor drop as an argument for con

Re: [ccp4bb] Twinning/Spacegroup Woes

As Aleks is suggesting, lower symmetry would be better. I had similar issues with one of my protein with unit cell dimensions 57, 57, 256. Xtriage suggested suggested three 2-fold merohedral twin operators (-h,-k,l; h,-h-k,-l; and –k,-h,-l). I went to lower symmetry (P31) and applied twinning law

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Re: [ccp4bb] Twinning/Spacegroup Woes

Dear Rhys, I was not aware that twinning is not possible in P6322 however I agree with Randy’s advise to check the lower symmetry P63 etc. We were just collecting data which was apparently P6322 (according to automated DLS processing: pointless) but the cell dimensions and our knowledge of the

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Re: [ccp4bb] Twinning/Spacegroup Woes

Dear Rhys, There's one important consideration to start from, which is that the space groups P6322 and C2221 with their associated cell dimensions are two different ways to describe the shapes of the unit cells and the positions of the spots. You can see this by running phenix.explore_metric_s