:term:`MRCC_OMP_NUM_THREADS <MRCC_OMP_NUM_THREADS (MRCC)>`
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      Sets the OMP_NUM_THREADS environment variable before calling MRCC. If the environment variable :envvar:`OMP_NUM_THREADS` is set prior to calling PSI4 then that value is used. When set, this option overrides everything. Be aware the ``-n`` command-line option described in section :ref:`sec:threading` does not affect MRCC. 

      * **Type**: integer
      * **Default**: 1