[Ifeffit] about wolframite crystallographic file

[Dominik Samuelis]

Dear Yordy,

this error message actually occured because the crystallographic data in 
the .cif file is somewhat ambigous. The space group is P 2/c (number 
13), which is a monoclinic cell (with two different settings, as 
additional complication: unique axis b or c).

Now, if you look in the .cif file, the unit cell parameters are given as 
follows:

-- snip
_cell_length_a                     4.6698(9)
_cell_length_b                     5.6873(23)
_cell_length_c                     4.9515(17)
_cell_angle_alpha                  90.
_cell_angle_beta                   90.(0)
_cell_angle_gamma                  90.
-- snip

You can see, that in the cif file, all angles are 90.0000 degrees. This 
however would be an orthorhombic cell, not a monoclinic. That's exactly 
the contents of the Artemis/Atoms error message:

"Monoclinic cells have all unequal axes and one non-right angle.
Unknown setting for a monoclinic cell.

Fatal error(s) in cell parameters."

The atoms code in this case is not able to determine the setting of the 
monoclinic cell, because it cannot find the unique axis. For humans, the 
unique axis is denoted by the standard deviation (0) behind beta, making 
it unique axis b. This however is not interpreted by Artemis.

This means, that you have to tell Artemis in some way, which angle 
deviates from 90°. For this, I usually change the beta angle in the cif 
file by some tiny amount, to -say- 90.0001 degrees. This is far below 
the standard deviation, so it's crystallographically still valid.

-- snip
_cell_angle_alpha                  90.
_cell_angle_beta                   90.0001(0)
_cell_angle_gamma                  90.
-- snip


Cheers,
dominik

Yordy Licea Fonseca wrote:
> Hi all,
>  
> As soon as I load this attached CIF crystallographic file from ISCD in 
> Artemis0.8.012 the software says:
> "Artemis trapped one or more errors!  Error message dumped to screen."
> I can`t go on runnig Atoms as it seems to be a problem with the file. I 
> have read the suggestion made in FAQ, but I can not manage to find the 
> error.
> Could you help me, please?
> It would be nice once the problem been fixed to add this structure to 
> Matt's atoms.inp database.
>  
> Thanks you very much, Yordy
> 
> -- 
> Yordy E. Licea Fonseca
> Departamento de Físico-Química
> Instituto de Química-IQ/UFRJ
> Laboratório de Catálise Heterogênea
> Rio de Janeiro, RJ, CEP 21.949-909
> Brasil
> Email: yliceafonseca at gmail.com <mailto:yliceafonseca at gmail.com>
> 
> 
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-- 
Dr. Dominik Samuelis
d.samuelis at fkf.mpg.de
Max-Planck-Institut für Festkörperforschung
Max Planck Institute for Solid State Research
Heisenbergstr. 1
70569 Stuttgart
Germany
Phone +49-711-689-1769
Fax   +49-711-689-1722
Web   http://www.fkf.mpg.de/maier/