[Wien] Site occupancy in multi-atom cell

[Shu Miao]

> No. There are 2 ways to approximate such a situation, but they have serious
> drawbacks:
>
> 1) use the virtual crystal approximation (VCA), in which you put an
> 'average' atom on a specific site. This can be done by changing the Z in
> case.struct. For your case, it would be Z=26.67 . You can imagine that this
> is a serious approximation, but because your elements have very similar Z,
> there might be something useful in it.
>
> 2) make your cell larger (e.g. 2x2x2), and put your 3 kinds of atoms
> randomly at their specific positions (and probably you'll have to relax the
> structure after that). Then, you have to repeat this for many different
> positions, and average the property you are interested in over all those
> calculations. You can imagine this is very time-consuming, especially
> because a 2x2x2 might be too small to accomodate all useful configurations,
> and you would need 3x3x3 or more.
>
> Is there a good reason why you want to use wien2k for your problem? If not,
> go to a code that has CPA implemented, which allows to do something like VCA
> but with a better physical foundation (still an approximation, however).
>
> Stefaan
>


Dear Stefaan and Jorissen,
Thanks for your suggestions. I want to use Wien2K only because it's
currently available on our cluster and it works very well in solving some
other materials. I want to use it to generate ELNES spectra to compare
with my experimental data. I have no experience in computational work.
Probably, I need to shift to other code.
Thanks

Shu Miao