MPI

The acronym MPI stands for Message Passing Interface.  Making use of the MPI libraries allows calculations to be split across many processors, leading to increased performance.  Only mdrun is MPI-enabled; none of the other utilities can be executed as parallel jobs.  With the introduction of threading in GROMACS version 4.5, external MPI libraries are not necessary to invoke a parallel calculation on a laptop, workstation or single compute node.