What does it mean for _diffrn_ambient_temperature and _cell_measurement_temperature to be different?

[Horst Puschmann]

Hello James,

I concur.

And I am almost certain that there is a mistake in most of the 1% where
there is a difference.

That _cell_measurement_temperature item should only really be present if
the temperature really *was* different -- a situation for which I can see
no reason why it should ever arise.

Horst




On Tue, 18 Jan 2022 at 05:47, James H via coreDMG <coredmg at iucr.org> wrote:

> 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.
>
> James.
>
> --
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