:term:`MPN <MPN (DETCI)>`
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      Do compute the MPn series out to kth order where k is determined by :term:`MAX_NUM_VECS <MAX_NUM_VECS (DETCI)>` ? For open-shell systems  :term:`REFERENCE <REFERENCE (DETCI)>` is ROHF, :term:`WFN <WFN (DETCI)>` is ZAPTN), DETCI will compute the ZAPTn series. :term:`GUESS_VECTOR <GUESS_VECTOR (DETCI)>` must be set to UNIT, :term:`HD_OTF <HD_OTF (DETCI)>` must be set to TRUE, and :term:`HD_AVG <HD_AVG (DETCI)>` must be set to orb_ener; these should happen by default for MPN = TRUE.

      * **Type**: :ref:`boolean <op_c_boolean>`
      * **Default**: false