# [Pw_forum] Phonons calculations at Gamma

Said Asma saidasma1987 at yahoo.fr
Tue Sep 30 18:49:54 CEST 2014

```Dear Nicola,
Thank you for your replay,
yes I've done the math with two atoms, but I'll make an alloy that is why I did it with 16 atoms.

Asma

***********************************************
Said Asma,
PhD. LMCN,
Faculté des sciences de Monastir,
Avenue de l'environnement 5019-Monastir,Tunisie
E-mail :saidasma1987 at yahoo.fr
***********************************************

Le Mardi 30 septembre 2014 17h43, Nicola Marzari <nicola.marzari at epfl.ch> a écrit :

Dear Said,

do the calculations with the primitive, 2-atom unit cell, on a mesh
of q-points, and plot the phonon dispersions. Otherwise in your supercell
the phonon branches get folded from the zone boundary to Gamma.

In the limit of q->0, you'll see three linear dispersions - two are
degenerate
and lower (the TA), one is higher (the LA). Check that they all go to zero
at q=0. Also, google "rocksalt phonon".

nicola

On 30/09/2014 18:25, Said Asma wrote:
> Dear QE users ans developers,
>
>
> I'm a beginner in the calculation of phonons.
> I did the phonons calculation of the binary AlN (rocksalt)  with 16 atoms .
>
> My output files is as following:
>
>     Diagonalizing the dynamical matrix
>
>       q = (    0.000000000   0.000000000   0.000000000 )
>
>   **************************************************************************
>       freq (    1) =       1.108833 [THz] =  36.986674 [cm-1]
>       freq (    2) =       1.574620 [THz] =      52.523675 [cm-1]
>       freq (    3) =       1.575398 [THz] =      52.549629 [cm-1]
>       freq (    4) =       8.195754 [THz] =     273.380916 [cm-1]
>       freq (    5) =       8.196815 [THz] =     273.416304 [cm-1]
>       freq (    6) =       8.199734 [THz] =     273.513674 [cm-1]
>       freq (    7) =       8.200351 [THz] =     273.534269 [cm-1]
>   freq (    8) =       8.201724 [THz] =     273.580054 [cm-1]
>       freq (    9) =       8.204042 [THz] =     273.657390 [cm-1]
>       freq (   10) =       8.204069 [THz] =     273.658277 [cm-1]
>       freq (   11) =       8.204305 [THz] =     273.666167 [cm-1]
>       freq (   12) =       9.560810 [THz] =     318.914296 [cm-1]
>       freq (   13) =       9.561375 [THz] =     318.933138 [cm-1]
>       freq (   14) =       9.564736 [THz] =     319.045240 [cm-1]
>       freq (   15) =       9.565551 [THz] =     319.072451 [cm-1]
>       freq (   16) =       9.568429 [THz] =     319.168422 [cm-1]
>       freq (   17) =       9.569095 [THz] =     319.190663 [cm-1]
>       freq (   18) =      12.351077 [THz] = 411.987578 [cm-1]
>       freq (   19) =      12.431223 [THz] =     414.660977 [cm-1]
>       freq (   20) =      12.439828 [THz] =     414.947983 [cm-1]
>       freq (   21) =      12.782122 [THz] =     426.365702 [cm-1]
>       freq (   22) =      12.796523 [THz] =     426.846069 [cm-1]
>       freq (   23) =      12.854425 [THz] =     428.777481 [cm-1]
>       freq (   24) =      12.908753 [THz] =     430.589665 [cm-1]
>       freq (   25) =  12.916648 [THz] =     430.852986 [cm-1]
>       freq (   26) =      12.923203 [THz] =     431.071665 [cm-1]
>       freq (   27) =      12.940057 [THz] =     431.633836 [cm-1]
>       freq (   28) =      12.951841 [THz] =     432.026913 [cm-1]
>       freq (   29) =      13.043933 [THz] =     435.098776 [cm-1]
>       freq (   30) =      13.090098 [THz] =     436.638683 [cm-1]
>       freq (   31) =      13.091268 [THz] =     436.677691 [cm-1]
>   freq (   32) =      16.509761 [THz] =     550.706361 [cm-1]
>       freq (   33) =      16.566717 [THz] =     552.606181 [cm-1]
>       freq (   34) =      16.587373 [THz] =     553.295203 [cm-1]
>       freq (   35) =      16.640103 [THz] =     555.054089 [cm-1]
>       freq (   36) =      16.658006 [THz] =     555.651280 [cm-1]
>       freq (   37) =      16.692001 [THz] =     556.785223 [cm-1]
>       freq (   38) =      19.936035 [THz] =     664.994532 [cm-1]
>       freq (   39) =      19.939099 [THz] =     665.096767 [cm-1]
>       freq (   40) =      19.940916 [THz] =     665.157356 [cm-1]
>       freq (   41) =      19.955181 [THz] =     665.633197 [cm-1]
>       freq (   42) =      21.966886 [THz] = 732.736442 [cm-1]
>       freq (   43) =      21.984557 [THz] =     733.325899 [cm-1]
>       freq (   44) =      22.013871 [THz] =     734.303712 [cm-1]
>       freq (   45) =      22.697394 [THz] =     757.103583 [cm-1]
>       freq (   46) =      22.729742 [THz] =     758.182599 [cm-1]
>       freq (   47) =      22.771292 [THz] =     759.568539 [cm-1]
>       freq (   48) =      22.788849 [THz] =     760.154171 [cm-1]
>   ***********************************************************************
>
> It has 16 atoms then we have 48 frequencies, 3 acoustic (which tend to
> 0) and 46 optical frenquencies, but how can I differentiate between
> longitudinal and transverse waves frequency?
> I looked at the file occurs, I found the displacements of atoms, but I
> was not able to distinguish between transeverse  and longitudinal
> optical modes.
>
> Below is an example of the frequencies in the dynamical matrix file :
>
>    freq (    4) =       8.195754 [THz] =     273.380916 [cm-1]
>   (  0.000000  0.000000 -0.044678  0.000000  0.044678  0.000000 )
>   (  0.000000  0.000000  0.002637  0.000000 -0.002637  0.000000 )
>   ( -0.164130  0.000000  0.393942  0.000000 -0.051695  0.000000 )
>   (  0.005529  0.000000  0.003753  0.000000  0.001833  0.000000 )
>   (  0.000000  0.000000  0.229388  0.000000 -0.229388  0.000000 )
>   (  0.000000  0.000000  0.001731  0.000000 -0.001731  0.000000 )
>   ( -0.167162  0.000000 -0.054230  0.000000  0.438521  0.000000 )
>   (  0.003854  0.000000 -0.000832  0.000000 -0.004534  0.000000 )
>   (  0.164130  0.000000  0.051695  0.000000 -0.393942  0.000000 )
>   ( -0.005529  0.000000 -0.001833  0.000000 -0.003753  0.000000 )
>   (  0.000000  0.000000 -0.188464  0.000000  0.188464  0.000000 )
>   (  0.000000  0.000000  0.006472  0.000000 -0.006472  0.000000 )
>   (  0.167162  0.000000 -0.438521  0.000000  0.054230  0.000000 )
>   ( -0.003854  0.000000  0.004534  0.000000  0.000832  0.000000 )
>   (  0.000000  0.000000  0.041543  0.000000 -0.041543  0.000000 )
>   (  0.000000  0.000000  0.004383  0.000000 -0.004383  0.000000 )
>       freq (    5) =       8.196815 [THz] =     273.416304 [cm-1]
>   (  0.553586  0.000000 -0.066816  0.000000 -0.066816  0.000000 )
>   ( -0.022611  0.000000 -0.004384  0.000000 -0.004384  0.000000 )
>   ( -0.050218  0.000000 -0.248855  0.000000 -0.082446  0.000000 )
>   ( -0.000781  0.000000  0.002840  0.000000  0.001799  0.000000 )
>   ( -0.187313  0.000000 -0.127347  0.000000 -0.127347  0.000000 )
>   (  0.002035  0.000000 -0.000907  0.000000 -0.000907  0.000000 )
>   (  0.049241  0.000000  0.085657  0.000000  0.277200  0.000000 )
>   ( -0.004321  0.000000 -0.001756  0.000000 -0.007275  0.000000 )
>   ( -0.050218  0.000000 -0.082446  0.000000 -0.248855  0.000000 )
>   ( -0.000781  0.000000  0.001799  0.000000  0.002840  0.000000 )
>   (  0.148869  0.000000  0.104419  0.000000  0.104419  0.000000 )
>   ( -0.007221  0.000000 -0.002029  0.000000 -0.002029  0.000000 )
>   (  0.049241  0.000000  0.277200  0.000000  0.085657  0.000000 )
>   ( -0.004321  0.000000 -0.007275  0.000000 -0.001756  0.000000 )
>   ( -0.498090  0.000000  0.065208  0.000000  0.065208  0.000000 )
>   (  0.005159  0.000000 -0.002368  0.000000 -0.002368  0.000000 )
>       freq (    6) =       8.199734 [THz] =     273.513674 [cm-1]
>   (  0.000000  0.000000 -0.016697  0.000000  0.016697  0.000000 )
>   (  0.000000  0.000000 -0.011124  0.000000  0.011124  0.000000 )
>   ( -0.282827  0.000000 -0.268330  0.000000 -0.074618  0.000000 )
>   (  0.007226  0.000000 -0.003886  0.000000  0.008910  0.000000 )
>   (  0.000000  0.000000  0.305360  0.000000 -0.305360  0.000000 )
>   (  0.000000  0.000000 -0.007286  0.000000  0.007286  0.000000 )
>   ( -0.279901  0.000000 -0.077837  0.000000 -0.279063  0.000000 )
>   (  0.009124  0.000000 -0.007508  0.000000  0.003791  0.000000 )
>   (  0.282827  0.000000  0.074618  0.000000  0.268330  0.000000 )
>   ( -0.007226  0.000000 -0.008910  0.000000  0.003886  0.000000 )
>   (  0.000000  0.000000 -0.292826  0.000000  0.292826  0.000000 )
>   (  0.000000  0.000000 -0.001182  0.000000  0.001182  0.000000 )
>   (  0.279901  0.000000  0.279063  0.000000  0.077837  0.000000 )
>   ( -0.009124  0.000000 -0.003791  0.000000  0.007508  0.000000 )
>   (  0.000000  0.000000  0.019674  0.000000 -0.019674  0.000000 )
>   (  0.000000  0.000000 -0.004853  0.000000  0.004853  0.000000 )
>
>
> with respectful regards
>
> ***********************************************
> Said Asma,
> PhD. LMCN,
> Faculté des sciences de Monastir,
> Avenue de l'environnement 5019-Monastir,Tunisie
> E-mail :saidasma1987 at yahoo.fr
> ***********************************************
>
>
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> Pw_forum at pwscf.org
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>

--

----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
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