47. Between NORMALPNO DLPNO-CCSD(T 0 ) and the corresponding multi-level variant, the relative energies differ by 1.2 kJ • mol -1 for the phenyl substituents and by 3.9 kJ • mol -1 for the mesityl substituents. However, the multi-level variant only requires 36% and 35%, respectively, of the computational time with respect to NORMALPNO DLPNO-CCSD(T 0 ). This is due to the reduced numbers of strong pairs which are included in the CCSD equations and the reduced numbers of triples.