[Ifeffit] Atoms and Feff for CuFe2O4 structure

[Bruce Ravel]

The first hit for spinel MgAl2O4 at crystallography.net gives these 
coordinates:

   Mg1   Mg2+   8 a 0. 0. 0. 1.  0 d
   Al1   Al3+  16 d 0.625 0.625 0.625 1.  0 d
   O1    O2-   32 e 0.375 0.375 0.375 1.  0 d

That's completely different from what's in the CIF file you sent.  Your 
cif file does not have Cu or O at symmetry positions associated with a 
spinel.  I suppose that makes sense given that your CIF file does not 
use the spinel space group.

It is true that Feff crashes, taking Artemis with it, when you try to 
run it on a list of atoms which has atoms that are 0.09 Angstroms apart. 
  I suppose that Artemis should recognize that situation and ask whether 
you really want to run Feff with such ridiculous input.  I'll put that 
on my to do list.

None of that answers your question of what to do.  You have some crazy 
structure that comes from who-knows-where, that is not a spinel, but 
which you think is a spinel.  I don't know what advice you are looking 
for, but you need to figure out your structure and make sure it runs to 
sensible completion in Atoms.

B

On 04/30/2014 01:55 PM, Qasim Imtiaz wrote:
> Dear all,
>
> I am using Atoms to calculate a Feff input file for CuFe2O4 spinel.
> However running Atoms/Feff results in program crash owing to 'two atoms
> very close together'. I modified the .cif file before importing (owing
> to partial occupancy issue) as following:
>
> Deleted: Fe2 Fe3+ 8 d 0.5 0.25 0.125 . 0.5 0
> Modified: Cu1 Cu2+ 8 d 0.5 0.25 0.125 . 0.5 0 to Cu1 Cu2+ 8 d 0.5 0.25
> 0.125 . 1 0
>
> After importing the file in Atoms, I also used different shift vectors
> (e.g. -0.125 -0.125 -0.125) but the issue is not resolved. Can someone
> help me please to solve this problem? Thanks.
> Best Regards
>
> Qasim
>
>
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-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
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