The first two approaches reduce cost in the triples correction of the quadruple-ζ calculation. This is typically the most costly part of the calculation, with the iterative (T 1 ) procedure taking significantly longer than (T 0 ). The first option is, thus, to correct DLPNO-CCSD(T 0 )/CBS (3,4) energies with the difference between (T 1 ) and (T 0 ) calculated with a smaller basis set: