[Pw_forum] Graphene phonon calculations too slow

[Paolo Giannozzi]

Are you sure you need that many k-points and such a big cell in the z
direction?
Attached a quick-and-dirty test. Parameters are likely far from yielding
converged values, but it takes 50' on a single processor of my 2007 vintage
PC. Before starting a full-fledged calculation at convergence, you should
experiment a bit. Also, tuning the parallelism may make a significant
difference.

Paolo

On Wed, May 25, 2016 at 5:13 PM, Abualnaja, Faris <
f.abualnaja15 at imperial.ac.uk> wrote:

> Dear all,
>
>
> I am running phonon calculations on graphene, and the calculations are
> taking days to complete! The calculations are run on a supercomputer and
> are running in parallel. I am using QE version 4.3.1, the amount of
> k-points that are calculated are 12x12x1 for an MP-grid which reduces down
> to 19 irreducible symmetry points. My phonon input is below:
>
>
> Phonon Dispersion of graphene
>
>  &inputph
>
>   recover=.true.
>
>   tr2_ph=1.0d-16
>
>   ldisp=.true.
>
>   nq1=12 nq2=12 nq3=1
>
>   prefix='graphene'
>
>   amass(1)=12.01
>
>   fildyn='graphene.dyn'
>
>  /
>
> and part of the output is shown here:
>
>
> Parallel version (MPI), running on    48 processors
>
>      K-points division:     npool     =    3
>
>      R & G space division:  proc/pool =   16
>
>                   :
>
>                   :
>
> Computing dynamical matrix for
>
>                     q = (   0.0000000   0.0000000   0.0000000 )
>
>      25 Sym.Ops. (with q -> -q+G )
>
>      G cutoff =  245.0079  (  16214 G-vectors)     FFT grid: ( 32, 32,600)
>
>      number of k points=   217  Methfessel-Paxton smearing, width (Ry)=
> 0.0100
>                   :
>                   :
>
> There are   4 irreducible representations
>
>
>      Representation     1      1 modes -B_2g To be done
>
>
>      Representation     2      2 modes -E_2g To be done
>
>
>      Representation     3      1 modes -A_2u To be done
>
>
>      Representation     4      2 modes -E_1u To be done
>                   :
>                   :
>
> G cutoff =  245.0079  ( 259459 G-vectors)     FFT grid: ( 32, 32,600)
>
>
>      Largest allocated arrays     est. size (Mb)     dimensions
>
>         Kohn-Sham Wavefunctions         0.34 Mb     (   2220,  10)
>
>         NL pseudopotentials             0.07 Mb     (   2220,   2)
>
>         Each V/rho on FFT grid          0.59 Mb     (  38912)
>
>         Each G-vector array             0.12 Mb     (  16224)
>
>         G-vector shells                 0.05 Mb     (   6856)
>
>      Largest temporary arrays     est. size (Mb)     dimensions
>
>         Auxiliary wavefunctions         1.35 Mb     (   2220,  40)
>
>         Each subspace H/S matrix        0.02 Mb     (     40,  40)
>
>         Each <psi_i|beta_j> matrix      0.00 Mb     (      2,  10)
>
>
>      The potential is recalculated from file :
>
>      ./_ph0/graphene.save/charge-density.dat
>
>
>      Starting wfc are    8 atomic +    2 random wfc
>
>
>      total cpu time spent up to now is      2.64 secs
>
>
>      per-process dynamical memory:    15.0 Mb
>
>
>      Band Structure Calculation
>
>      Davidson diagonalization with overlap
>
>      c_bands:  1 eigenvalues not converged
>
>      c_bands:  1 eigenvalues not converged
>
>      c_bands:  1 eigenvalues not converged
>
>      c_bands:  1 eigenvalues not converged
>
>      c_bands:  1 eigenvalues not converged
>
>
>      ethr =  1.25E-10,  avg # of iterations = 63.7
>
>
>      total cpu time spent up to now is   4392.92 secs
>
>
>      End of band structure calculation
>
>                   :
>                   :
>
> Any suggestions on how to speed up the process and if I am missing
> something?! Thank you in advance for all your kind help and time.
>
> Regards,
>
> Faris
> Imperial
>
>
>
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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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