[Pw_forum] DFT+U calculations

[Muhammad Adnan]

Dear Mostafa
Thank you for your detailed answer.
you wrote 'In fact, although literature clearly shows that DFT+U predicts
qualitatively problematic phonon dispersion for soft-mode materials such as
TiO2'
could you please cite some references? i tried to find some, but i could
not find any source to validate the claim.
thanks
Adnan

On Thu, Aug 13, 2015 at 3:56 AM, Mostafa Youssef <myoussef at mit.edu> wrote:

> Dear Muhammad ,
>
> This is really tricky. Using DFT+U for 0K energies followed by DFT for
> phonons is a bit inconsistent.  I would rather be consistent and understand
> the limitations of the theory rather than trying to mix inconsistent parts
> together.
>
> You could ignore the vibrational contribution as suggested by Jia Chen ,
> although I think at high temperature this contribution might be
> significant. Alternatively you could resort to the extremely expensive
> hybrid functionals  to do both 0K energies and phonons (within frozen
> phonon approximation). Another sound alternative is just to use DFT+U for
> 0K energies and phonons with the clear understanding that therer might be
> some error associated with the phonons part.  In fact, although literature
> clearly shows that DFT+U predicts qualitatively problematic phonon
> dispersion for soft-mode materials such as TiO2 , there has not been a
> systematic investigation of the performance of DFT+U in predicting
> vibrational free energy *differences* between a perfect crystal (TiO2) and
> a defective one (TiO2-x) for this class of materials.  I would be very
> interested if somebody can point out to a paper that addressed this.
>
>
> Mostafa Youssef
> MIT
>
> <http://www.mail-archive.com/search?l=pw_forum@pwscf.org&q=from:%22Muhammad+Adnan%22>
>
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-- 
Best Regards
Muhammad Adnan Saqlain
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