CFOUR_ABCDTYPE

Specifies the way the $$\langle ab||cd \rangle$$ 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 $$\langle ab||cd\rangle$$ integrals. AOBASIS (=2) uses an AO-based algorithm to evaluate all terms involving the $$\langle ab||cd\rangle$$ 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