:term:`CFOUR_ABCDTYPE <CFOUR_ABCDTYPE (CFOUR)>`
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      Specifies the way the :math:`\langle ab||cd \rangle` molecular orbital integrals are handled in post-MP2 calculations. STANDARD (= 0) uses directly the corresponding MO integrals and thus results in an algorithm which in particular for large-scale calculations results in excessive use of disk space (storage of all :math:`\langle ab||cd\rangle` integrals. AOBASIS (=2) uses an AO-based algorithm to evaluate all terms involving the :math:`\langle ab||cd\rangle` integrals and significantly reduces the amount of disk storage. The use of ABCDTYPE=AOBASIS is strongly recommended for all CC calculations up to CCSD(T) and has been implemented for energy, gradient, second-derivative, and excitation energy calculations.

      * **Type**: string
      * **Possible Values**: STANDARD, AOBASIS
      * **Default**: STANDARD