[Pw_forum] Reg: q is not a vector in the dense grid.

[Sridhar Sadasivam]

If you want to compute electron-phonon interaction for a phonon of
wavevector q, you will need electron wavefunctions at k and k+q. Thus your
grid for scf should always be a multiple of your q-point grid for phonon
calculations. Since 8 is a multiple of 2 and 4 but not 6, you are getting
this error. Hope that helps.
Sridhar
Purdue University


On Sun, Jun 1, 2014 at 9:36 AM, Peram sreenivasa reddy <
peramsreenivas at gmail.com> wrote:

> Dear Pwscf,
>
>
> In my phonon calculations i got some error.
>
> For nq1=2, nq2=2, nq3=2 and nq1=4, nq2=4, nq3=4 i did not get any errors.
>
> But for nq1=6, nq2=6, nq3=6 grid i got the bellow error.
>
> Diagonalizing the dynamical matrix
>
>      q = (   -0.166666667   0.166666667  -0.166666667 )
>
>  **************************************************************************
>      omega( 1) =       1.218152 [THz] =      40.633179 [cm-1]
>      omega( 2) =       1.218152 [THz] =      40.633179 [cm-1]
>      omega( 3) =       2.760322 [THz] =      92.074433 [cm-1]
>      omega( 4) =       3.157206 [THz] =     105.313054 [cm-1]
>      omega( 5) =       3.157206 [THz] =     105.313054 [cm-1]
>      omega( 6) =       3.160843 [THz] =     105.434373 [cm-1]
>      omega( 7) =       6.119555 [THz] =     204.126381 [cm-1]
>      omega( 8) =       6.129602 [THz] =     204.461528 [cm-1]
>      omega( 9) =       6.129602 [THz] =     204.461528 [cm-1]
>      omega(10) =       9.495441 [THz] =     316.733825 [cm-1]
>      omega(11) =       9.521102 [THz] =     317.589790 [cm-1]
>      omega(12) =       9.521102 [THz] =     317.589790 [cm-1]
>  **************************************************************************
>
>      Mode symmetry, C_3v (3m)   point group:
>
>      omega(  1 -  2) =         40.6  [cm-1]   --> E    L_3
>      omega(  3 -  3) =         92.1  [cm-1]   --> A_1  L_1
>      omega(  4 -  5) =        105.3  [cm-1]   --> E    L_3
>      omega(  6 -  6) =        105.4  [cm-1]   --> A_1  L_1
>      omega(  7 -  7) =        204.1  [cm-1]   --> A_1  L_1
>      omega(  8 -  9) =        204.5  [cm-1]   --> E    L_3
>      omega( 10 - 10) =        316.7  [cm-1]   --> A_1  L_1
>      omega( 11 - 12) =        317.6  [cm-1]   --> E    L_3
>
>  **************************************************************************
>      electron-phonon interaction  ...
>
>
>
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>      from elphsum : error #         3
>      q is not a vector in the dense grid
>
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
>      stopping ...
>
>
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>      from elphsum : error #         3
>      q is not a vector in the dense grid
>
>  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> This error came after completing my first q point.
>
>
> Is this q grid is correct for the given k points mesh?
>
> Is it better to increase it to nq1=8, nq2=8, nq3=8. ?
>
> Thank you very much in advance.
>
>
>
>
>
>
>
> --
> *P.V.SREENIVASA REDDY*
>
> *Research ScholarDepartment of Physics *
>
>
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