Dear Konrad
to my understanding OpenMP can be used when parallelizing within a multicore node. It needs shared memory between the cores so can't/shouldn't be used to parallelize across different nodes. MPI does not need shared memory and can be used both inside a multicore node and across nodes.
   HTH
stefano

On 19/09/2016 12:01, Konrad Gruszka wrote:

Dear colleagues,

I'm Writing to our community to clarify once and for all issues with parallel pwscf execution.

By lecture of PWSCF manual, I know that there are several levels of parallelization, including FFTW and more. At the same time, I'm quite sure that most of beginner QE users do not have complicated clusters, but are rather starting with decent multicore PC's.

There are two main parallel mechanisms (known to me) namely: MPI and OpenMP. Because I'm using Ubuntu, there is free Hydra MPI software (mpich) and also free OpenMP. From what I know (please correct me if this is wrong) MPI software is used for parallelization within one multicore PC and OpenMP is used to make parallelization between several PC's.

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