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RE: Using _atom_site_disorder_* data names to describe compositionaldisorder?

  • To: "james.r.hester@gmail.com" <james.r.hester@gmail.com>, "Distribution listof the IUCr COMCIFS Core Dictionary Maintenance Group" <coredmg@iucr.org>
  • Subject: RE: Using _atom_site_disorder_* data names to describe compositionaldisorder?
  • From: "Bollinger, John C via coreDMG" <coredmg@iucr.org>
  • Date: Wed, 10 Nov 2021 17:34:41 +0000
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I not only have no objection, I think it is essential to make that allowance to accommodate a large body of traditional practice.  Popular crystallographic refinement programs that emit CIF (SHELXL, for example) do not provide distinct mechanisms for modelling these different varieties of disorder, and they do emit CIF using the _atom_site_disorder_* data names to describe the results.


Moreover, I’m not convinced that there is a clean distinction between these disorder types.  For example, when there is a compositional disorder involving elements with significantly different size or different charge, it is not so unusual for that to be correlated with changes in the positions of the neighboring atoms, which are sometimes resolvable.








John C. Bollinger, Ph.D., RHCSA

Computing and X-Ray Scientist

Department of Structural Biology

St. Jude Children's Research Hospital


(901) 595-3166 [office]





From: coreDMG <coredmg-bounces@iucr.org> On Behalf Of James H via coreDMG
Sent: Tuesday, November 9, 2021 6:58 PM
To: Distribution list of the IUCr COMCIFS Core Dictionary Maintenance Group <coredmg@iucr.org>
Cc: James H <jamesrhester@gmail.com>
Subject: Using _atom_site_disorder_* data names to describe compositional disorder?


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Dear Core DMG,


It has been noticed [1] that the _atom_site_disorder_* data names, which are designed to describe positional disorder of a group of bonded atoms, could also be used to describe compositional disorder, where one site is randomly occupied by one of two (or more) atom types. Vol G First edition describes two other methods for recording compositional disorder, and only talks of positional disorder of a group of atoms when discussing the _atom_site_disorder_* data names. It seems clear that these data names were designed with groups of atoms in mind, but nothing seems to explicitly exclude using them for compositional disorder.


The question for you all is, are there any objections or problems any of you can see with explicitly allowing compositional disorder to be described using _atom_site_disorder_* data names?





[1] https://github.com/COMCIFS/cif_core/issues/251

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