:term:`ICORE <ICORE (DETCI)>`
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      Specifies how to handle buffering of CI vectors. A value of 0 makes the program perform I/O one RAS subblock at a time; 1 uses entire CI vectors at a time; and 2 uses one irrep block at a time. Values of 0 or 2 cause some inefficiency in the I/O (requiring multiple reads of the C vector when constructing H in the iterative subspace if :term:`DIAG_METHOD <DIAG_METHOD (DETCI)>` = SEM), but require less core memory.

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

