[Pw_forum] Could not find the mode symmetry after phonon frequency calculation of gamma point

[Sitangshu Bhattacharya]

Dear Zhishuo,

You can see the mode information when verbosity is high in scf output
(report) file. I am sorry, if the pictures are not visible. Here is a
result with a certain pseudo operating on ibrav 4 crystal structure:
     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     freq (    1) =      -0.917705 [THz] =     -30.611333 [cm-1]
     freq (    2) =       0.892747 [THz] =      29.778839 [cm-1]
     freq (    3) =       0.892747 [THz] =      29.778839 [cm-1]
     freq (    4) =       5.229748 [THz] =     174.445607 [cm-1]
     freq (    5) =       5.229748 [THz] =     174.445607 [cm-1]
     freq (    6) =       7.453800 [THz] =     248.632002 [cm-1]
     freq (    7) =       7.453800 [THz] =     248.632002 [cm-1]
     freq (    8) =       7.469963 [THz] =     249.171131 [cm-1]
     freq (    9) =       9.218972 [THz] =     307.511813 [cm-1]
 **************************************************************************

     Mode symmetry, D_3h (-62m) point group:

     freq (  1 -  1) =        -30.6  [cm-1]   --> A''2            I
     freq (  2 -  3) =         29.8  [cm-1]   --> E'              I+R
     freq (  4 -  5) =        174.4  [cm-1]   --> E''             R
     freq (  6 -  7) =        248.6  [cm-1]   --> E'              I+R
     freq (  8 -  8) =        249.2  [cm-1]   --> A'_1            R
     freq (  9 -  9) =        307.5  [cm-1]   --> A''2            I


And here is the result done on the same structure with another pseudo with
same constraint on same structure:
     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     freq (    1) =       0.215200 [THz] =       7.178313 [cm-1]
     freq (    2) =       0.254327 [THz] =       8.483433 [cm-1]
     freq (    3) =       0.510191 [THz] =      17.018144 [cm-1]
     freq (    4) =       5.050369 [THz] =     168.462168 [cm-1]
     freq (    5) =       5.074174 [THz] =     169.256234 [cm-1]
     freq (    6) =       7.173385 [THz] =     239.278353 [cm-1]
     freq (    7) =       7.187844 [THz] =     239.760658 [cm-1]
     freq (    8) =       7.251512 [THz] =     241.884398 [cm-1]
     freq (    9) =       8.954276 [THz] =     298.682514 [cm-1]
 **************************************************************************

     Mode symmetry, C_2v (mm2)  point group:

     freq (  1 -  1) =          7.2  [cm-1]   --> A_1  D_1  S_1   I+R
     freq (  2 -  2) =          8.5  [cm-1]   --> B_2  D_4  S_4   I+R
     freq (  3 -  3) =         17.0  [cm-1]   --> B_1  D_3  S_3   I+R
     freq (  4 -  4) =        168.5  [cm-1]   --> A_2  D_2  S_2   R
     freq (  5 -  5) =        169.3  [cm-1]   --> B_2  D_4  S_4   I+R
     freq (  6 -  6) =        239.3  [cm-1]   --> A_1  D_1  S_1   I+R
     freq (  7 -  7) =        239.8  [cm-1]   --> B_1  D_3  S_3   I+R
     freq (  8 -  8) =        241.9  [cm-1]   --> A_1  D_1  S_1   I+R
     freq (  9 -  9) =        298.7  [cm-1]   --> B_2  D_4  S_4   I+R

Both the pseudos are norm conserving. Clearly, the 1st pseudo detects the
mode symmetry correctly. Increasing more harder constraint results the 9
modes to converge and produces the correct dispersion, but the mode
symmetry is somehow wrongly read in the 2nd case. I am using QE v 6.1.
THere are few options to get rid of imaginary freqencies: Relax the
structure well in the order of 10^-6 or less. Do the phonon on a supercell.
Change your ASR to a different value. Compare the lattice constants with
the available experimental data.

Regards,
Sitangshu

On Tue, Jan 9, 2018 at 5:49 PM, 黄志硕 <zhishuohuang at gmail.com> wrote:

> Dear Prof. Sitangshu Bhattacharya,
>
>
>
> Thank you for your reply. But what do you mean by ‘scf report file’? Is it
> the output file of scf calculation? I don’t see the symmetry information in
> the output file of scf calculation.
>
>
>
> For the pseudopotential, I tested them. The consistent between the AE
> energy and PS energy is well as well as the logarithmic derivatives. I also
> tested them in band-structure calculations, and they also produced nearly
> the same band structures with other PPs provided by quantum espresso PP
> library. And the phonon dispersion calculated with these PPs seem
> reasonable.
>
>
>
> And by the way, I could not view the pictures you posted.
>
>
>
> Best regards
>
> Zhishuo Huang
>
>
>
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> Pw_forum at pwscf.org
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>



-- 
**********************************************
Sitangshu Bhattacharya (সিতাংশু ভট্টাচার্য), Ph.D
Assistant Professor,
Room No. 2221, CC-1,
Nanoscale Electro-Thermal Laboratory,
Department of Electrical and Communication Engineering,
Indian Institute of Information Technology-Allahabad
Uttar Pradesh 211 012
India
Telephone: 91-532-2922000 Extn.: 2131
Web-page: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
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