[Pw_forum] A strange problem in phonon calculation

[Paolo Giannozzi]

You can make a calculation at a q point that has imaginary 
frequencies, verify if you get the same result or if it is 
an artifact of Fourier interpolation 

P.

On Tue, 2013-06-18 at 09:38 +0800, Wei-Bing Zhang wrote:
> Dear all
>  
> 
> Recently, I am trying to calculate the phonon dispersion of 2D
> materials. I used 4x4x1 q-points in phonon calculation whereas a
> 16x16x1 k-points for self-consistent electronic calculation. The
> direct calculations indicate that all phonons frequencies are above
> zero on the grid of q-vectors including the Gamma point. However, when
> I transformed the dynamical matrices from G- to R-space and calculated
> phonon dispersions using “matdyn.x”, some negative frequencies appear
> in acoustic mode ZA near Gamma point.  Since I am really a new user
> for phonon calculation, I am not sure what happened. The input and
> output file are enclosed. Could you tell me what’s wrong with my
> calculations? Any suggestions will be appreciated. 
> 
>  
> 
> Thanks and best regards
> 
>  
> 
> Wei-Bing Zhang
> 
>  
> 
> 
> ----------------------------------------------------------------------
> 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
> ----------------------------------------------------------------------
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222