[QE-users] Gamma point phonon calculation is not consistent

[Paolo Giannozzi]

There are two sets of "differences" in your calculations:
- the three lowest frequencies of the acoustic mode
- symmetry labels B_2 and B_3.
I don't know about the latter, but the former difference reflects an
algorithmic difference: the Gamma-only code (phcg.x) imposes acoustic sum
rule during the calculation, while the ordinary phonon code (ph.x) doesn't.
Nothing to worry about.

Paolo

On Wed, Oct 30, 2019 at 3:16 AM wang1968000 <wang1968000 at 163.com> wrote:

> Hi. QE users.
> I have calculate Gamma point phonon and phonon dispersion on black
> phosphorus.
> But the phonon modes are not same in only Gamma point calculation and
> several q point calculations.
>
> This is the results coming from only Gamma point calculation.
>  Diagonalizing the dynamical matrix
>
>      q = (    0.000000000   0.000000000   0.000000000 )
>
>  **************************************************************************
>      freq (    1) =      -0.038897 [THz] =      -1.297458 [cm-1]
>      freq (    2) =      -0.031677 [THz] =      -1.056638 [cm-1]
>      freq (    3) =       0.027926 [THz] =       0.931519 [cm-1]
>      freq (    4) =       2.928955 [THz] =      97.699418 [cm-1]
>      freq (    5) =       5.638698 [THz] =     188.086708 [cm-1]
>      freq (    6) =       6.639162 [THz] =     221.458590 [cm-1]
>      freq (    7) =      10.953491 [THz] =     365.369131 [cm-1]
>      freq (    8) =      12.684841 [THz] =     423.120746 [cm-1]
>      freq (    9) =      12.722708 [THz] =     424.383866 [cm-1]
>      freq (   10) =      12.745234 [THz] =     425.135234 [cm-1]
>      freq (   11) =      13.570613 [THz] =     452.666939 [cm-1]
>      freq (   12) =      13.874216 [THz] =     462.794044 [cm-1]
>  **************************************************************************
>
>      Mode symmetry, D_2h (mmm)  point group:
>
>      freq (  1 -  1) =         -1.3  [cm-1]   --> B_3u            I
>      freq (  2 -  2) =         -1.1  [cm-1]   --> B_1u            I
>      freq (  3 -  3) =          0.9  [cm-1]   --> B_2u            I
>      freq (  4 -  4) =         97.7  [cm-1]   --> B_3u            I
>      freq (  5 -  5) =        188.1  [cm-1]   --> B_3g            R
>      freq (  6 -  6) =        221.5  [cm-1]   --> B_2g            R
>      freq (  7 -  7) =        365.4  [cm-1]   --> A_g             R
>      freq (  8 -  8) =        423.1  [cm-1]   --> A_u
>      freq (  9 -  9) =        424.4  [cm-1]   --> B_1g            R
>      freq ( 10 - 10) =        425.1  [cm-1]   --> B_2g            R
>      freq ( 11 - 11) =        452.7  [cm-1]   --> A_g             R
>      freq ( 12 - 12) =        462.8  [cm-1]   --> B_1u            I
>
>
> This results comes from Gamma point  in several q point calculation.
>       q = (    0.000000000   0.000000000   0.000000000 )
>
>  **************************************************************************
>      freq (    1) =       0.294821 [THz] =       9.834157 [cm-1]
>      freq (    2) =       0.531839 [THz] =      17.740255 [cm-1]
>      freq (    3) =       0.538183 [THz] =      17.951848 [cm-1]
>      freq (    4) =       2.934902 [THz] =      97.897792 [cm-1]
>      freq (    5) =       5.651273 [THz] =     188.506166 [cm-1]
>      freq (    6) =       6.641297 [THz] =     221.529834 [cm-1]
>      freq (    7) =      10.953478 [THz] =     365.368700 [cm-1]
>      freq (    8) =      12.689602 [THz] =     423.279546 [cm-1]
>      freq (    9) =      12.724636 [THz] =     424.448167 [cm-1]
>      freq (   10) =      12.750003 [THz] =     425.294313 [cm-1]
>      freq (   11) =      13.570944 [THz] =     452.677974 [cm-1]
>      freq (   12) =      13.879876 [THz] =     462.982823 [cm-1]
>  **************************************************************************
>
>      Mode symmetry, D_2h (mmm)  point group:
>
>      freq (  1 -  1) =          9.8  [cm-1]   --> B_1u            I
>      freq (  2 -  2) =         17.7  [cm-1]   --> B_3u            I
>      freq (  3 -  3) =         18.0  [cm-1]   --> B_2u            I
>      freq (  4 -  4) =         97.9  [cm-1]   --> B_2u            I
>      freq (  5 -  5) =        188.5  [cm-1]   --> B_2g            R
>      freq (  6 -  6) =        221.5  [cm-1]   --> B_3g            R
>      freq (  7 -  7) =        365.4  [cm-1]   --> A_g             R
>      freq (  8 -  8) =        423.3  [cm-1]   --> A_u
>      freq (  9 -  9) =        424.4  [cm-1]   --> B_1g            R
>      freq ( 10 - 10) =        425.3  [cm-1]   --> B_3g            R
>      freq ( 11 - 11) =        452.7  [cm-1]   --> A_g             R
>      freq ( 12 - 12) =        463.0  [cm-1]   --> B_1u            I
>
>
> Why these two parts are not same?
> The structure I already optimised.
>
> TW.
> Department of Physics
> Tohoku Unviersity
> Email: wang1968000 at 163.com
>
>
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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