Running a calculation in parallel
=================================

ORCA can run in multiple processors with the aid of `OpenMPI <https://www.open-mpi.org/>`_ (the recommended version for ORCA 5 is 4.1.1). After installing it and setting the PATH and LD_LIBRARY_PATH variables (what is that? :ref:`path_variable`), you can simply run in parallel using the PAL keyword. For instance, a calculation using four processors requires::

   !HF DEF2-SVP PAL4
   
For more than eight processors (!PAL8), the explicit %PAL option has to be used::

   !HF DEF2-SVP
   %PAL NPROCS 16 END
   
When running calculations in parallel, always use the full path to ORCA::

   ./full/path/to/orca input.inp   
   
.. important::

   Always install the OpenMPI version indicated in the Download section!