[phenixbb] Dual conformation on symmetry axis

[Jrh]

Hello Pavel and Tim,
I think the 'special nature of artefacts at a symmetry position' are special in that the electron density there is naturally amplified and therefore looks worse than it really is. Otherwise your points are well taken.
Greetings,
John 

Emeritus Prof of Chemistry John R Helliwell DSc_Physics 
https://www.crcpress.com/Perspectives-in-Crystallography/Helliwell/9781498732109
A new book which resonates with the recent UN, UNESCO and IUCr International Year of Crystallography.

On 5 Feb 2016, at 15:35, Pavel Afonine <pafonine at lbl.gov> wrote:

> Hi,
> 
>> density on symmetry elements usually displays artefacts and is difficult to
>> interpret.
> 
> I've seen this rumor perpetuated so many times.. I think I can also say "Fourier maps show artifacts anywhere in the unit cell volume (including symmetry elements) that originate, for example, from: a) finite resolution and partial completeness of the data, b) errors in crystal structure model (model is always used as a source of phase information), c) measurement errors. These artifacts are difficult (and unnecessarily) to interpret in terms of atomic model.". Are symmetry elements somewhat special in this regard (that is one sees more artifacts on symmetry elements than anywhere else)? If this is the case, can someone provide convincing reasoning for this (not hand-waving!)?
> 
> Thanks,
> Pavel
> 
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