[Wien] Huge volume variation in volume optimization

[Peter Blaha]

> I am trying to work on volume optimization of a doped material, CdSiAsBi.

No, you are NOT studying a "doped" material, you study an artificially 
ordered CdSiAsBi compound. 50% doping is not a doping.

And: yes, Bi is much larger than As, so most likely a large volume is ok.

And: Your E-vol curve does not look good (very noisy, the data points 
are not on the fitted line.

And: if you really want to study THIS structure, you should also do 
optimization of internal positions as the Bi/As atoms want to move 
around ...

> The base material was CdSiAs2 and then it was doped with a bismuth atom (in a 1x1x1 supercell).
> The structure thus changes from tetragonal body centred (CdSiAs2) to orthorhombic body centred (CdSiAsBi).
> I tried doing the volume optimization with constant a:b:c ratio (option 1) and it took a pretty large volume percent variation to obtain an energy minimum in the energy vs. volume plot.
> As can be seen from the ps file and optimize.job, I had to vary the volume upto 32% to obtain a decent curve. Somehow this much of volume variation does not look okay to me. Can I proceed with this or is there a problem with it? Is this much of volume variation okay?
> I have attached the structure files, optimize.job and energy vs. vol plots for reference.
>
> regards,
>
> Ushma Ahuja
> Faculty of Engineering
> M. L. Sukhadia University
> Udaipur, India
>
>
>
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                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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