[Pw_forum] negative frequency in high q-mesh

[Wei-Bing Zhang]

Dear Prof. Giannozzi

Thanks very much for your quick reply.  The "unreasonable" just means
there are few negative frequencies in acoustic phonon. Based on the
published results about silicene (Phys. Rev. Lett. 102, 236804
(2009)), the silicene should be stable. On the other hand, as shown in
the phonon spectrum of q-mesh (9, 9, 1) enclosed in the last message,
the negative frequencies are only found in Gamma-K and M-Gamma region.
So it seems to be induced some insufficient convergence or wrong
setting of some parameters.  However, I can’t get rid of it.

Wei-Bing


On 31 January 2013 17:03, Paolo Giannozzi <giannozz at democritos.it> wrote:
> On Thu, 2013-01-31 at 15:32 +0800, Wei-Bing Zhang wrote:
>
>> Unfortunately, I can only get the reasonable phonon dispersion
>> with q-mesh below 6x6x1
>
> what makes you think that the results with denser q-mesh
> are unreasonable? Are you sure that silicene is mechanically
> stable? if not, there can be phonons with negative (actually
> imaginary) frequency
>
> P.
> --
> Paolo Giannozzi, IOM-Democritos and University of Udine, Italy
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum



-- 
----------------------------------------------------------------------
Dr. Wei-Bing Zhang

School of Physics and Electronic Sciences
Changsha University of Science and Technology,
Changsha,  People’s Republic of China
Phone : +86 186 73108538
E-mail: zwb256 at hotmail.com, weibingzhangavh at gmail.com
----------------------------------------------------------------------