[Wien] optimising volume for hematite

[Torsten Andersen]

Dear Chandrika,

Chandrika wrote:
> Hello,
> I have written about this problem before but am still stuck. So please 
> help oncemore.
>  
> I optimised hematite (Fe2O3) which has the same space group as Al2O3 
> (167 R-3c). I used the structure file in "Examples" of Wien and the 
> experimental values of cell parameters (a=b=5.035 Ang, c= 13.747 Ang, 
> angles, 90). The optimised volume is around -10 to -12%, whatever the 
> exchange functional I use (13, 5, 14). I did both c/a and vol 
> optimisation for all these. I also did this with spin-orbit coupling. 
> The volumes come very far from experimental. Band gap is also too small 
> (~ 0.3eV). (I used 600 k points, RMT= 1.8 for Fe and 1.6 for O).
>  
> My question is :
> (i) Will Wien  not work for a strongly correlated system like Fe2O3?

Probably only with LDA+U, if at all. But a theoretical value of -10% in 
the volume can also be acceptable if the important properties come out 
right...

> (ii) Can I change the inst file to reflect the actual oxidation state of 
> Fe (3+) and O (2-). In this case Fe would have only 5 outer electrons 
> (Ar, 3d5) and O would have He, 2s2, 2p6.

I can't see why not. Try it out.

Best regards,
Torsten Andersen.

> Is it permitted to change the inst file and transfer 3 electrons from Fe 
> to O? This may be a silly question but I do not know.
> Thank you for your time,
> Chandrika
>  
>  
> -----------------------------------------------------------------------------------
> Dr (Ms) Chandrika Varadachari
> Raman Centre for Applied and Interdisciplinary Sciences
> 16 A Jheel Road
> Calcutta 700075
> India
>  
> Tel : 91-33-24830029
> Fax 91-33-24180610
> 
> 
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-- 
Dr. Torsten Andersen        TA-web: http://deep.at/myspace/
AG Hübner, Department of Physics, Kaiserslautern University
http://cmt.physik.uni-kl.de    http://www.physik.uni-kl.de/