It is worth noting that tight PNO thresholds add significantly to the cost of DLPNO calculations. For RI-MP2 calculations on our hardware, the (C 96 H 24 ) 2 system that is explored in Section III H represents an approximate crossover point for loose-MP2 thresholds. That calculation requires 614 min for RI-MP2/cc-pVDZ with the DLPNO approximation, running on 40 processors with 4.5 Gb of memory per processor, which should be compared to 617 min for the canonical calculation on 48 processors with 5.0 Gb per processor. As the PNO thresholds are tightened, that 614 min calculation on 40 processors for T CutPNO = 10 -7 becomes 4,825 min for T CutPNO = 10 -8 and 6,531 min for T CutPNO = 10 -9 . It should be noted that we have set the integral threshold as conservatively as possible (10 -16 a.u.) for the purpose of benchmarking, and more aggressive integral screening may shift the crossover point in favor of the DLPNO approach. Furthermore, CCSD(T) calculations will reach the crossover point in smaller system sizes. A systematic timing study is beyond the scope of the present work, however.