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Re: What does it mean for _diffrn_ambient_temperature and_cell_measurement_temperature to be different?

  • 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: What does it mean for _diffrn_ambient_temperature and_cell_measurement_temperature to be different?
  • From: "Spek, A.L. \(Ton\) via coreDMG" <coredmg@iucr.org>
  • Date: Tue, 18 Jan 2022 09:19:08 +0000
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A good point. 
IUCr/PLATON/checkCIF sends out an A-level ALERT for this. Referees should have picked this up.
Older SHELXL versions put in a default value for those values in the CIF they generated (Room Temperature)
A quick check of the CIF's for all structures published in the 2021 issues of Acta Cryst. E77 shows that there are no inconsistencies there.

Best wishes


Op 18-01-2022 06:47 heeft coreDMG namens James H via coreDMG <coredmg-bounces@iucr.org namens coredmg@iucr.org> geschreven:

    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 may
    have been a difference in the past when using point detectors and the
    cell was determined separately to the data collection, but for
    anything collected on an area detector I would have expected these
    values to be the same. However, I've noticed from looking at around
    10000 files from the COD that, of the files that have both data names,
    around 1% have different numbers. I'm wondering what this could
    possibly mean, especially when the two numbers are very different e.g.
    150K and 296K. Given that the cell parameters are necessary to obtain
    absolute distances from fractional coordinates, if the diffraction
    data are collected at a different temperature to the cell measurement,
    then surely these atomic distances would be incorrect?  How do the
    database curators handle this? How are software authors interpreting
    these two data names for output or input?

    If you agree that there is no way these numbers should be
    significantly different, suggestions on how to fix the situation are
    welcome. Personally I would deprecate _cell_measurement_temperature or
    state that it is only used when the cell is measured separately to the
    main diffraction data set.


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