I don't know what the return on investment would be, but after establishing that there are cell dimension deviations one should actually try to find the source of the problem. If it is the reported geometry of the experiment than it is just a matter of changing the cell dimension, but if the wavelength come into play as Clemens pointed out (hooray for home sources) one should also correct the wavelength in order to get better scattering factors. If you don't have ice rings as a reference can you still do that? Perhaps refine f' and f''. Has anyone does that in a systematic way?
Cheers, Robbie > -----Original Message----- > From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Eleanor > Dodson > Sent: Thursday, July 16, 2020 12:57 > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Quote source inquiry > > 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 > <vonrh...@globalphasing.com <mailto:vonrh...@globalphasing.com> > > 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 > > ######################################################## > ################ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA- > JISC.exe?SUBED1=CCP4BB&A=1 > > This message was issued to members of www.jiscmail.ac.uk/CCP4BB > <http://www.jiscmail.ac.uk/CCP4BB> , a mailing list hosted by > www.jiscmail.ac.uk <http://www.jiscmail.ac.uk> , terms & conditions are > available at https://www.jiscmail.ac.uk/policyandsecurity/ > > > > ________________________________ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
