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Crystal mosaicity

  • To: coredmg@iucr.org
  • Subject: Crystal mosaicity
  • From: Brian McMahon via coreDMG <coredmg@iucr.org>
  • Date: Tue, 9 Jul 2024 14:48:03 +0100
  • Cc: Brian McMahon <bm@iucr.org>
I am working with the NanED group on extensions to CIF for 3D electrondiffraction. Since some of them are using dynamical refinement, theyroutinely report crystal mosaicity, but we are surprised to find thatthere is not a term for this in the core dictionary. The PDBx/mmCIFdictionary does have this definition:
save__exptl_crystal.pdbx_mosaicity    _item_description.description;    The of the distribution of mis-orientation angles specified in degrees    of all the unit cells in the crystal. Lower mosaicity indicates better    ordered crystals.;    _item.name                  '_exptl_crystal.pdbx_mosaicity'    _item.category_id             exptl_crystal    _item.mandatory_code          no    _item_type.code               float    _item_units.code              degrees     save_

A few questions:
(1) Is a data name for crystal mosaicity useful in the core dictionary?
(2) Is the definition in the pdbx dictionary correct and mostappropriate. (No doubt the first sentence should read "The distributionof...", or perhaps "A measure of the distribution...")
(3) I am told that the ED people determine a numeric value (in degrees,as per the pdbx definition) from inspection of the rocking curve. Isthis the standard way to determine mosaicity, or do we need additionalitems to explain how it was determined?
Comments welcome,Brian_________________________________________________________________________
Brian McMahonInternational Union of Crystallography            e-mail:  bm@iucr.org5 Abbey Square, Chester CH1 2HU, England_______________________________________________coreDMG mailing listcoreDMG@iucr.orghttp://mailman.iucr.org/cgi-bin/mailman/listinfo/coredmg

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