[Pw_forum] Negative Phonon Frequencies - Numerical instability or unstable structure

[Pietro Delugas]

Hello Mohammed


If the phonon were computed with phononpy for any numerical problem 
maybe you will find more help in the forum of phononpy users.


Could you provide more information about the structure ?  Is it 3D or 2D ?



greetings - pietro


On 05/12/2016 08:23, Mohammed Ghadiyali wrote:
>
> Dear All,
>
>
> I am working on a bilayer tin system and has performed geometry 
> relaxation using Quantum Espresso 5.4.0 of the structure via:
>
>
>
> 1. One relax calculation - for coordinate relaxation
>
>
> 2. One vc-relax calculation with cell_do_free as 2Dxy - for coordinate 
> and cell shape relaxation
>
>
> 3. Two vc-relax calculation with cell_do_free as shape - for 
> coordinate and cell shape relaxation with constant volume.
>
>
>
> these calculations were performed with, ecutwfc = 60 Ry and K-point 
> mesh as 10 10 1, 1 1 1.
>
>
> Further, phonon calculations were performed using the phononpy 1.11.0 
> package with the same parameters. The
>
>
> structure seem to gotten relaxed but it still has some negative 
> frequencies near the Gamma point, are these's negative
>
>
> frequencies numerical instabilities or the structure is unstable.
>
>
>
> I am attaching the phonon dispersion file. Please advice.
>
>
>
> Regards,
>
>
> Ghadiyali Mohammed Kader.
>
>
> Research Scholar,
>
>
> University of Mumbai.
>
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20161205/931134d5/attachment.html>