[Pw_forum] DFT+U calculations

[Mostafa Youssef]

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>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150812/3abfb43c/attachment.html>