[Cod-bugs] Issues found in a systematic scanning of the COD

[Caussin, Pierre]

Hi there,

I am working for Bruker and trying to better streamline the use of the COD in our search/match and semiquantitative software. One of the goals is being able to compute the peak positions and relative intensities and RIR of COD entries. We do this at CuKA1 wavelength for all the entries that have a structure and space group given (all entries except 1119 that have either no atomic coordinates and/or blank or unknown space group, which are currently ignored). This compilation is done using the symmetries stored in the CIF file.

To be able to compute the selected entries at other wavelengths on the fly, we need the space group symmetries, without keeping the complete CIFs, which use over 26GB after ZIP compression. I have written code to create a table [space group HM name] => [table of symmetries]. This works well, but I have found 478 CIF files where the given HM name appears to contradict the list of symmetries. I enclose the diagnostic output of my program (plus my case-by-case comment '//'), which can be summarized in two cases:


  1.  The list of symmetries is obviously wrong or contradicts the Bravais symbol in the group name
  2.  The list of symmetries is plausible but either is erroneous or does not match the most common space group settings (axes and origin). This is not a problem if I rely on the CIF list but causes a conflict if I have other phases using the same space group in the 'usual' settings. I can handle this by adding a character to the group name when the phase originates in the COD.

Thank you for your attention, best regards,

Pierre Caussin


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