[Ifeffit] [IFEFFIT] question about chemically unordered systems

[Scott Calvin]

Hi Falk,

These pages may help:

http://cars.uchicago.edu/ifeffit/FAQ/FeffitModeling?highlight=%28doping%29#How_do_I_handle_doped_materials.3F_Why_doesn.27t_Atoms_handle_doped_materials.3F

http://cars.uchicago.edu/ifeffit/Doped

http://cars9.uchicago.edu/~ravel/software/doc/Atoms/Atoms/node4.html#SECTION00440000000000000000

--Scott Calvin
Sarah Lawrence College

On Aug 7, 2012, at 10:52 AM, Meutzner, Falk wrote:

> Dear Matt, dear community
> 
> thank you for your fast reply!
> I am not sure, if I understand you correctly. I tried what you suggested, but 
> the result is just the same. I will try to give some more insight:
> 
> Our binary system is bcc (pm-3m), there is one atom on the position (0,0,0) 
> and another one on the position of (0.5,0.5,0.5).
> After creation of the material, we have a chemically disordered state. Any of 
> the two atoms can occupy any of the aforementioned positions.
> After heat treatment however, the material chemically orders itself and 
> becomes CsCl structure. In theory, atom A will always be on the corner at 
> (0,0,0), while atom B will always be in the centre of the cell at 
> (0.5,0.5,0.5).
> 
> Our problem is, we would like to distinguish between these two phases, because 
> we possibly have mixtures of the ordered and disordered states.
> 
> We already achieved the ordered state with atoms, because they are unique 
> positions (Atom A at (0,0,0), atom B at (0.5,0.5,0.5). Unfortunately we are 
> unsure how to model the disordered state. We would need the possibility to 
> tell the programme, that the observed atom will always be A at (0,0,0), while 
> the other atom has a possibility of 50% to be A and 50% to be B.
> 
> For the programme it seems not to matter which of the positions our observed 
> atom is at. Therefore the calculated spectra are the same.
> 
> I hope I was able to give more insight into our problem.
> Thank you! Best Regards
> Falk