[Ifeffit] ATOMS: Partial occupancies -how to edit .cif File

[Carlo Segre]

Hi Kai:


On Tue, 23 Apr 2013, Sanwald, Kai wrote:

>
> 1. changed occupancy from 0.5 to 1 in line
> Ni1 Ni2+ 16 d 0.625 0.625 0.625 . 0.5 0
>
> 2. subsequently deleted line
>
> Fe2 Fe3+ 16 d 0.625 0.625 0.625 . 0.5 0
>
>
> I got rid of the ATOMS warning concerning the partial occupancy but FEFF6 crashes due to atoms being postioned too closely to each other. I am pretty sure that my editing resulted in a change of the structure.
>
> I would be very glad if someone could explain to me in some detail how I need to edit the .cif.
>

No, you did not change anything in the structure and you did the correct 
thing to generate a cluster.  However this space group has two settings, 
separated by (1/8 1/8 1/8) and the standard setting that you get from 
ATOMS is the wrong one for these atomic positions.  It gives a Ni-O 
distance of less than 1Angstrom.  if you put in the shift vector, of
(-0.125 -0.125 -0.125) it will work fine and you will get reasonable 
distances.

Carlo



-- 
Carlo U. Segre -- Duchossois Leadership Professor of Physics
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org