[Wien] optimising volume for hematite

[Chandrika]

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? 
(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.
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


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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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