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 <cdf...@gmail.com> 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 <kell...@janelia.hhmi.org>
> 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: kell...@janelia.hhmi.org
>>
>> *******************************************
>>
>>
>>
>
>

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