Dear William, Thank you so much for your answer, it was very helpful,
Alejandro On Wed, March 28, 2012 2:47 pm, William Parker wrote: > Dear Alejandro, > > The images in phonon calculations are groupings of the irreducible > representations of the phonon modes. Hence, the maximum number of images > is the number of representations. > > There is a speedup as one increases the number of images parallelized > over, but the speedup increases irregularly with image number since > different representations require different amounts of time to calculate. > In my limited experience, the time taken by single representations can > vary at least up to a factor of two. > > The second step does generate all of the right dynamical matrix entries, > but I have been unable to get the recover step to complete successfully > yet, though I am currently working on this (if anyone else on the list has > any comments on this, please speak up). > > Running on parallel with one image but parallelizing over k-points and FFT > grid works properly. I don't have any experience with the GRID method so > perhaps someone else can say something about that. > > I'm not aware of any more documentation beyond what you quoted. > > A simple example I run my tests on is two-atom Si with a 2x1x1 q-mesh (two > q-points, six representations), parallelizing over two images. > With only one CPU per k-point pool, the commands look like: > > mpiexec -n 1 pw.x -npool 1 -inp si.scf.cg.in >& si.scf.cg.out > mpiexec -n 2 ph.x -nimage 2 -npool 1 -inp si.ph.in >& si.ph.out > mpiexec -n 1 ph.x -nimage 1 -npool 1 -inp si.ph_recover.in >& > si.ph_recover.out > > where "diff si.ph.in si.ph_recover.in" returns "recover = .true." > > --William > > On Mar 28, 2012, at 1:34 PM, Alejandro R?bola wrote: > >> Dear all, >> >> I'm trying to run phonon calculations using ph.w on a cluster (NERSC), >> and >> since I have a big number of atoms I wanted to parallelize it as much >> and >> efficiently as possible. I've been reading the documentation, and I've >> seen the GRID example, I was going to use this but then I saw the >> following at the end of the INPUT_PH.html file: >> >> On parallel machines the q point and the irreps calculations can be >> split >> automatically. The procedure is the following: >> >> " [...] >> >> 1) run pw.x with nproc processors and npools pools. >> 2) run ph.x with nproc*nimage processors, npools pools and nimage >> images. >> 3) run ph.x with the same input and recover=.true. on nproc processors >> and npools pools and only one image. >> >> During the first ph.x run the phonon code split the total amount of >> work into nimage copies. Each image runs with different q and/or >> representations. The second run of ph.x is the final run that >> collects all the data calculated by the images and writes the files >> with the dynamical matrices." >> >> Since I'm not very familiar with the terminology used here (I'm >> completely >> lost) I would like to ask some questions: >> 1) If I'm running on a cluster like NERSC, would I get any advantage >> from >> using the GRID method or should I just use the method outlined above? >> 2) In that case, what does it mean by images for a phonon calculation >> (I'm >> just familiar with images for NEB). Where could I find more >> documentation >> about this or some example? >> Thank you in advance, >> >> Alejandro R?bola >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://www.democritos.it/mailman/listinfo/pw_forum > > ********************************************************* > William D. Parker phone: (630) 252-4834 > Computational Postdoctoral Fellow fax: (630) 252-4798 > MSD-212, Rm. C-215 > Argonne National Laboratory > 9700 S. Cass Ave. > Argonne, IL 60439 > ********************************************************* > > > > > >
