[Pw_forum] A strange problem in phonon calculation

[Duy Le]

Did you perform the test for q-mesh? I would do 2x2x1, 3x3x1 and
higher (if it is not that expensive) to see the evolution of
phonon-dispersion. Usually, 4x4x1 q-mesh is enough for converged
dispersion.


----------------------------------------------------
Duy Le
Postdoctoral Associate
Department of Physics
University of Central Florida.
Website: http://www.physics.ucf.edu/~dle


On Wed, Jun 19, 2013 at 4:45 PM, Paolo Giannozzi
<paolo.giannozzi at uniud.it> wrote:
> 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
>
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