Sorry--I think you were referring to phasing, not refinement. I hope my message is still relevant.
Cheers, Chris On Tue, Oct 11, 2016 at 10:39 AM, Chris Fage <[email protected]> wrote: > Dear Jacob, > > I'm not an expert on the topic, but from my experiences with twinning I > can agree with you. I recently solved my second twinned structure by MR > (twin fraction of 0.43, as estimated by Xtriage). Performing twin > refinement in Refmac or phenix.refine dropped the R-factors, as expected, > but worsened the geometry considerably without a noticeable improvement in > the maps. For this reason, I opted *not* to go with the twin refinement... > I don't know if others would make the same choice, though it seemed > reasonable to me. Besides, my Rwork/Rfree is down to 0.25/0.29, which ain't > too shabby for 2.6 A resolution. > > Cheers, > Chris > > On Tue, Oct 11, 2016 at 2:15 AM, Keller, Jacob <[email protected]> > wrote: > >> Dear Crystallographers, >> >> >> >> Based on some data sets I have looked at and anecdotal-type evidence here >> and there I have gotten the impression that detwinning does not help in >> structure solution. (Please let me know if you have a case where detwinning >> saved the day.) Is there a clear answer to this enigma anywhere, to >> anyone’s knowledge? Wouldn’t it seem that **any** detwinning would be >> better than **no** detwinning? I understand that the errors explode as >> one approaches 50% twins and does detwinning, but still, I don’t think one * >> *loses** information by detwinning, right? Take the case of a 33% twin: >> since the twin-reflections are on average about half the intensity of the >> non-twin, and since they are generally not correlated in intensity, isn’t >> this like having noise added at 50% of the measured intensity? So why does >> detwinning make things worse generally? Is there something wrong in the >> assumptions underlying the detwinning algorithm, or perhaps something about >> the calculation that throws things off? >> >> >> >> A related sub-enigma: why is MR generally immune to twinning, but >> anomalous methods are susceptible? >> >> >> >> All the best, >> >> >> >> Jacob Keller >> >> >> >> ******************************************* >> >> Jacob Pearson Keller, PhD >> >> Research Scientist >> >> HHMI Janelia Research Campus / Looger lab >> >> Phone: (571)209-4000 x3159 >> >> Email: [email protected] >> >> ******************************************* >> >> >> > >
