[Pw_forum] Hubbard U

[Giuseppe Mattioli]

Dear Tommaso
Regarding the metal ions, Matteo Cococcioni already answered your question: you can use the same supercell to calculate both the linear response 
values. Regarding the O, it is often useful/mandatory to use an on-site correction in transition metal oxides, because if you correct only the metal 
you may completely miss the p-d coupling. But a reasonable estimate of the U value for O is not very easy. You may be interested in this paper, which 
investigates the double U(Ti,O) correction in intrinsic and defective TiO2:

Mattioli, et al.; J. Phys. Chem. C 2010, 114, 21694.

J. J. Gong pointed out some days ago an alternative method to estimate the ab initio U value in fully occupied (or almost fully occupied) bands, which 
is often the case of O 2p bands in oxides. It could be interesting to know the opinion of the QE "U-developers" on the possibility to implement the 
related Hartree-Fock calculation. Anyway the method is discussed here:

Mosey, et al.; J. Chem Phys. 2008, 129, 014103

Finally, the implementation of the U+V correction (see Leiria Campo and Cococcioni; J. Phys.: Condens. Matter 2010, 22, 055602), which would be very 
useful in covalent compounds, should be added to the next QE release. For a comprehensive review, you may also be interested in:

Himmetoglu, et al.; Int. J. Quantum Chem. 2014, 114, 14.

HTH

Giuseppe

On Wednesday 28 May 2014 23:10:46 Tommy wrote:
> Dear all,
> i'm working on a Yttria doped Zirconia, YSZ. I have understood how to
> calculate the U values for a single site, but how can i calculate the U
> values for both the transition metal inside the same structure, e.g. Zr
> and Y in YSZ structure? Do i have to build a supercell even in this case?
> Do you think that i need to calculate also the oxygen U contribute? Sorry
> for the trivial question, but I'm deeply interested in the method and
> understand every feature. Thanks in advance,
> Tommaso Francese.
> Università Cà Foscari of Venice.


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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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