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 <adnansaql...@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 <myous...@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 ! >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum@pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > -- > Best Regards > Muhammad Adnan Saqlain > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum >
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