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

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.

--
T +61 (02) 9717 9907
F +61 (02) 9717 3145
M +61 (04) 0249 4148
_______________________________________________
coreDMG mailing list
coreDMG@iucr.org
http://mailman.iucr.org/cgi-bin/mailman/listinfo/coredmg