[Wien] To count the no. of atom if occupancy is 0.5 - reg

[Peter Blaha]

Hi,

Your system is a disordered system and has a structure with "fractional 
occupancy" 0.5.

This is a valid approach to characterize an average structure as it 
comes out from an X-ray diffraction experiment.

However, in reality of course on a particular position in space there is 
an atom or there is none. Thus in the simulation you have to resemble 
this disorder by manually remove half of those Cu2 atoms (in a random 
way), until your stoichiometry is correct. This will break symmetry and 
of course lower the space group in the simulations.

When the unit cell is small, the results may critically depend on your 
choice of removed atoms. Then you must create supercells and remove 
again half of the atoms in a random way.


Am 24.09.2020 um 19:13 schrieb Chriz:
> Sir,
>       Good evening. We are working with fd-3m structured ternary 
> compound. The details are attached in the image.  This structure is got 
> from experimental paper.
> In this structure,
> 
> Cu1 atom sits in 8b position which generate 2 atoms with occupancy 
> mentioned by reference paper as 1.
> Cu2 atom sits in 48f position which generates 12 atoms with occupancy 0.5.
> 
> Mn in 16c generate 4 atoms with occupancy 1.
> 
> Te in 32e generate 8 atoms with occupancy 1.
> 
> If we write the formula we get Cu14 Mn4 Te8. But this is actually 
> Cu4Mn2Te4 which is contradict.
> 
> Our question is how to treat Cu2 atom with occupancy 0.5 *Should we 
> consider Cu2 generates 6 atom instead 12 as its occupancy is 0.5.*
> 
> Kindly clarify the doubt.
> 
> Thanks in advance.
> 
> Regards,
> Viswa.
> 
> 

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