[Pw_forum] DFT+U calculations

[Jia Chen]

Dear Muhammad Adnan,

Firstly, I would like to point out contribution of vibrational modes to
free energy would not be significant compared to the uncertainties coming
for other parts of calculation. Because you don't have a light element,
like H, in your system.

Secondly, It may be quite tricky to calculation vibrational frequencies
using DFT+U, particularly for systems like TiO2-1, even with frozen phonon
method. Because small displacement of atoms in these systems can cause
dramatic change of electronic structure.

Cheers

On Wed, Aug 12, 2015 at 4:49 PM, Muhammad Adnan <adnansaqlain at gmail.com>
wrote:

> Dear Mostafa
> Thanks for pointing out my mistake in the title of the email.
> Actually, I need to compute DeltaG, DeltaH and DeltaST for the reaction,
> TiO2 --> TiO2-1 + 1/2O2.
> for this, i need vibrational frequencies of TiO2 and TiO2-1. If relax the
> surfaces with DFT+U and then use simply DFT calculations for calculating
> frequencies, what would be the effect on frequencies?
>
> On Wed, Aug 12, 2015 at 8:02 PM, Mostafa Youssef <myoussef at mit.edu> wrote:
>
>> Hi Adnan,
>>
>>
>> The effect of DFT+U on the phonon dispersion of materials with soft-modes
>> such as TiO2 is large. Not only quantitatively but also qualitatively.  See
>> for example:
>>
>> http://www.sciencedirect.com/science/article/pii/S1567173910004682
>>
>>
>> and figure 8 in:
>>
>> http://iopscience.iop.org/0953-8984/26/12/122203/
>>
>>
>> If your main goal is to study phonons of TiO2 , I would recommend LDA or
>> PBEsol.  But if you insist on using DFT+U , then you can use PHONOPY +
>> PWscf code of Q.E equipped with a *large* supercell of TiO2.  This should
>> allow you to calculate phonon dispersion in frozen phonon approximation
>> with Parlinski et al interpolation.  Please follow the instructions on
>> PHONOPY website.
>>
>>
>> Mostafa YOussef
>> MIT
>> P.S. Somehow I read the title of your thread as DFT+U cartoons !
>>
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>>
>
>
>
> --
> Best Regards
> Muhammad Adnan Saqlain
>
>
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