:term:`GUESS_VECTOR <GUESS_VECTOR (DETCI)>`
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      Guess vector type. Accepted values are ``UNIT`` for a unit vector guess  :term:`NUM_ROOTS <NUM_ROOTS (DETCI)>` and :term:`NUM_INIT_VECS <NUM_INIT_VECS (DETCI)>` must both be 1); ``H0_BLOCK`` to use eigenvectors from the H0 BLOCK submatrix (default); ``DFILE`` to use NUM_ROOTS previously converged vectors in the D file; ``IMPORT`` to import a guess previously exported from a CI computation (possibly using a different CI space) 

      * **Type**: string
      * **Possible Values**: UNIT, H0\_BLOCK, DFILE, IMPORT
      * **Default**: H0\_BLOCK