:term:`REFERENCE_SYM <REFERENCE_SYM (DETCI)>`
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      Irrep for CI vectors; -1 = find automatically. This option allows the user to look for CI vectors of a different irrep than the reference. This probably only makes sense for Full CI, and it would probably not work with unit vector guesses. Numbering starts from zero for the totally-symmetric irrep. 

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