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What does it mean for _diffrn_ambient_temperature and_cell_measurement_temperature to be different?

  • To: Distribution list of the IUCr COMCIFS Core Dictionary Maintenance Group<coredmg@iucr.org>
  • Subject: What does it mean for _diffrn_ambient_temperature and_cell_measurement_temperature to be different?
  • From: James H via coreDMG <coredmg@iucr.org>
  • Date: Tue, 18 Jan 2022 16:46:47 +1100
  • Cc: James H <jamesrhester@gmail.com>
Happy New Year everybody.
Here is our first issue for the year:
At first glance it would appear to me that _diffrn_ambient_temperature and_cell_measurement_temperature are describing the same thing. There mayhave been a difference in the past when using point detectors and thecell was determined separately to the data collection, but foranything collected on an area detector I would have expected thesevalues to be the same. However, I've noticed from looking at around10000 files from the COD that, of the files that have both data names,around 1% have different numbers. I'm wondering what this couldpossibly mean, especially when the two numbers are very different e.g.150K and 296K. Given that the cell parameters are necessary to obtainabsolute distances from fractional coordinates, if the diffractiondata are collected at a different temperature to the cell measurement,then surely these atomic distances would be incorrect?  How do thedatabase curators handle this? How are software authors interpretingthese two data names for output or input?
If you agree that there is no way these numbers should besignificantly different, suggestions on how to fix the situation arewelcome. Personally I would deprecate _cell_measurement_temperature orstate that it is only used when the cell is measured separately to themain diffraction data set.
-- T +61 (02) 9717 9907F +61 (02) 9717 3145M +61 (04) 0249 4148_______________________________________________coreDMG mailing listcoreDMG@iucr.orghttp://mailman.iucr.org/cgi-bin/mailman/listinfo/coredmg

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