[Pw_forum] Parallel bandstructure calculations

[Gabriele Sclauzero]

Il giorno 23/ago/2010, alle ore 16.32, Nicki Frank Hinsche ha scritto:

> Hi there,
> 
> I am currently doing calculations of iso-energy surfaces on doped  
> semiconductors. Therefore I generate with an external program a quite  
> big k-point mesh for which I want to determine the eigenvalues and  
> later on construct the iso-energy surface with a tetrahedron method.  
> My problem is the running time of the bandstructure calculation.
> 
> The size of the unit (super)-cells is in the order of 30-50 atoms,  
> containing 1 or 2 different atomic species. For k-points in the order  
> of 4000-6000 the eigenvalues have to be calculated (most often around  
> 50-100 ev's for each k-point).
> 
> 
> After the scf-calculation is done quite fast, I am running the nscf  
> bandstructure calc. with the command
> 
> 
> mpirun -np 32 pw.x -npool 4 -diag 16


The correct version of this command line should be 

mpirun -np 32 pw.x -npool 4 -ndiag 16

but this would not work either since ndiag must be smaller or equal to nproc/npool (which is 8 in your case). So you should either use

mpirun -np 32 pw.x -npool 4 -ndiag 4

or

mpirun -np 64 pw.x -npool 4 -ndiag 16


I suggest you to use this in combination with scalapack libraries, since it may improve a lot the speed when the number of bands is very large (as in your case).

If this isn't fast enough for your needs, probably you'll have to switch to another method, such as Shirley's interpolation for instance (see http://arxiv.org/abs/0908.3876).


HTH

GS

> 
> 
> but the calculation isn't done parallel, as the output says:
> 
>      Parallel version (MPI), running on    32 processors
>      K-points division:     npool     =    4
>      R & G space division:  proc/pool =    8
> 
>      Subspace diagonalization in iterative solution of the eigenvalue  
> problem:
>      a serial algorithm will be used


§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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