# CFOUR_ABCDTYPE

> Specifies the way the 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 integrals. AOBASIS (=2) uses an AO-based algorithm to evaluate all terms involving the 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