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5 Parallelism

We refer to the corresponding section of the PWscf guide for an explanation of how parallelism work.

ph.x may take advantage of MPI parallelization on images, plane waves (PW) and on k-points (''pools''). Currently all other MPI and explicit OpenMP parallelizations have very limited to nonexistent implementation. phcg.x implements only PW parallelization. All other codes may be launched in parallel, but will execute on a single processor.

In ``image'' parallelization, processors can be divided into different "images", corresponding to one (or more than one) "irrep" or wave-vector in phonon calculations. Images are loosely coupled: processors communicate between different images only once in a while, so image parallelization is suitable for cheap communication hardware (e.g. Gigabit Ethernet). Image parallelization is activated by specifying option -nimage N to ph.x. Inside an image, PW and k-point parallelization can be performed: for instance,

   mpirun -np 64 ph.x -nimage 8 -npool 2 ...
will run 8 images on 8 processors each, subdivided into 2 pools of 4 processors for k-point parallelization.

A different paradigm is the usage of the GRID concept, instead of MPI, to achieve parallelization over irreps and wave-vectors. Complete phonon dispersion calculation can be quite long and expensive, but it can be split into a number of semi-independent calculations, using options start_q, last_q, start_irr, last_irr. An example on how to distribute the calculations and collect the results can be found in examples/GRID_example. Reference:
Calculation of Phonon Dispersions on the GRID using Quantum ESPRESSO, R. di Meo, A. Dal Corso, P. Giannozzi, and S. Cozzini, in Chemistry and Material Science Applications on Grid Infrastructures, editors: S. Cozzini, A. Laganà, ICTP Lecture Notes Series, Vol. 24, pp.165-183 (2009).


next up previous contents
Next: 6 Troubleshooting Up: User's Guide for the Previous: 4.3 Calculation of electron-phonon   Contents
Layla Martin-Samos Colomer 2012-05-10