[Wien] position of f-orbitals

[Rocquefelte]

Yes there is but at the end it will be not far from DFT+U results.

Indeed, Fabien Tran and Peter Blaha, at least, have implemented in 
WIEN2k a series of hybrid approaches.

In particular, you can use the semi-local hybrid potential modified 
Becke-Johnson potential to have proper band gaps (as good as GW and some 
times better).
However, in your case, I believe that this choice is not the best (I 
only believe, it could be interesting to do a test ...).

Another possibility is to use onsite-hybrid functionals, which will lead 
to a similar result than DFT+U. Indeed in this implementation, only the 
chosen orbitals in the atomic spheres will be corrected (onsite 
correction for a specific orbital as in DFT+U).
This is a good choice because for realistic systems (many atoms) the 
calculations are nearly as expensive as a regular LDA calculation.

Finally, you have the possibility to use the full-hybrid functional. 
Here the correction is applied to all atoms and orbitals.
This last solution is very expensive in terms of calculation time 
compared to an LDA calculation. Thus I imagine that in your case (doped 
insulators) it will be quite tricky to realize such calculations.

These comments are based on my own experience and need to be completed 
by more experts people in this field. But I hope it will help you.

Best Regards

Xavier


Le 26/10/2012 10:01, hiroshi.nakano at sharp.co.jp a écrit :
>
> Dear all
>
> I am calculating rare-earth doped insulators.
>
> The materials should have f-orbital between the host materials' 
> bandgap in density of states(DOS).
>
> Experiment supports this fact.
>
> However, in some cases, the DOS calculated with WIEN2k does not put 
> f-orbital inside the host materials' bandgap.
>
> Basically, I calculated with GGA functional and have already applied 
> DFT+U.
>
> I get some f-orbital stayed in the valence band of host materials.
>
> In this case, the energy of f-orbitals are underestimated.
>
> In other case, f-orbitals are inside the conduction band of host 
> materials, that is, overestimated.
>
> My questions are:
>
> Does these kinds of situation usually happen in f-orbitals?
>
> Are there any good way to calculate f-orbitals precisely except DFT+U 
> in WIEN2k?
>
> Best Regards,
>
> Nakano
>
>
>
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