Hi Eleanor,
Yes, I remember those meetings, when the UK was still an EU member and Sweden
not yet (so Uppsala couldn't be formally involved) :-)
Did Victor look into this too? I remember Gert doing it. And maybe Tom
Oldfield?
Best wishes,
--Gerard
On Thu, 16 Jul 2020, Eleanor Dodson wrote:
> Hmm - remember Gerard, the EU Validation initiative in the 1990s? We
> analysed these effects, or at least Victor Lamsin did, and we applauded him.
> Cheers Eleanor
>
> On Thu, 16 Jul 2020 at 11:52, Clemens Vonrhein <[log in to unmask]>
> wrote:
>
>> Hi Robbie,
>>
>> On Wed, Jul 15, 2020 at 07:23:15PM +0000, Robbie Joosten wrote:
>>> At the same time if you have a a more relaxed approach to restraints
>>> than you might find systematic deviations in bond lengths. A test
>>> for that has been in WHAT_CHECK for decades and it actually works
>>> surprisingly well to detect cell dimension problems.
>>
>> Indeed.
>>
>>> That said, the problem is uncommon now.
>>
>> Not so sure about that: we all rely on an accurate value of the
>> energy/wavelength from the instrument/beamline - and if that is off
>> (for whatever reasons) it will result in incorrect cell dimensions and
>> a systematic deviation from the various restraints.
>>
>> This would even affect the best experiment done on the best crystal
>> ... so fairly easy to spot at the refinement stage, especially if such
>> an energy/wavelength offset is constant over a long period of time on
>> a given instrument. To spot this at the data collection stage one
>> would hope that at some point a crystal with very pronounced ice-rings
>> will be looked at properly (and the fact these are not where we expect
>> them to should cause some head-scratching).
>>
>> Cheers
>>
>> Clemens
>>
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Best wishes,
--Gerard
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Gerard J. Kleywegt
http://xray.bmc.uu.se/gerard mailto:[log in to unmask]
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