[Wien] regarding case.struct generation

[Alexander Alexander]

Dear Farshad,

The fractional occupancy could usually be treated either by making a
supercell which is a bit expensive as usually a big cell would be required
or by a method called virtual crystal approximation (VCA) that work well
mostly for the neighboring atoms but it might works in your case as Ni and
Fe are not far a way from each other in the periodic table of element, just
google virtual crystal approximation ! you will find more details.

Cheers,
Salman


On Mon, Feb 8, 2016 at 2:32 PM, Farshad Nejadsattari <fneja083 at uottawa.ca>
wrote:

> Dear Professor Blaha, Wien2k community and experts,
>
>    I am working on the compound Al72Ni9Fe19. This system crystallizes in
> the space group P63/mmc (No. 194). Two of the Wyckoff sites are partially
> occupied by Fe and Ni atoms, I would like to know how to construct the
> master input file, (case.struct) for this system since both atoms occupy
> the same Wyckoff sites but with different proportions. I have looked
> through the mailing list and have not found anything particular regarding
> this type of problem. The atomic positions are given below:
>
> *Atom**                                             Wyckoff Site
>                                       (x,y,z)*
>
> Al(1)                                                   2*a*
>                                              (0,0,0)
> Al(2)                                                   6*h*
>                                              (0.4647,0.9294,0.25)
> Al(3)                                                   12*k
>                                              *(0.1935,0.3870,0.9392)
> 0.6786Fe(1)+0.3114Ni(1)                       2*d*
>                                    (1/3,2/3,3/4)
> 0.6786Fe(2)+0.3114Ni(2)                       6*h*
>                                    (0.1256,0.2512,0.25)
>
>      As seen above, the iron and nickel atoms occupy the Wyckoff sites at
> an approximate 2/1 (Fe/Ni) ratio. Your assistance towards constructing the
> case.struct file for this compound is truly appreciated.
>
> With regards,
>
> Farshad Nejadsattari,
> PhD candidate in condensed matter physics,
> University of Ottawa, Canada
>
>
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