:term:`CFOUR_SCF_EXTRAPOLATION <CFOUR_SCF_EXTRAPOLATION (CFOUR)>`
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      Specifies whether or not the DIIS extrapolation is used to accelerate convergence of the SCF procedure. OFF (=0) means do not use DIIS, ON (=1) means use DIIS.

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

