:term:`CFOUR_CC_EXTRAPOLATION <CFOUR_CC_EXTRAPOLATION (CFOUR)>`
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      Specifies the type of convergence acceleration used to solve the CC equations. RLE (=0) uses the RLE methods of Purvis and Bartlett, DIIS (=1) uses the DIIS approach by Pulay, NOJACOBI (=2) uses RLE with continuous extrapolation, OFF (=3) uses no convergence acceleration. In general, DIIS provides the best results and is recommended, while OFF often results in poor convergence and thus cannot be recommended.

      * **Type**: string
      * **Possible Values**: RLE, DIIS, NOJACOBI, OFF
      * **Default**: DIIS