In the first step, we examine the impact of individual pair selection thresholds in detail for a set of reactions which was already studied with the pair-selected multi-level DLPNO-CCSD(T 0 ) method, yet based on the DOS scheme. In Fig. , the effect of different pair selection thresholds for multi-level DLPNO-CCSD(T 0 ) with a target accuracy of NORMALPNO is shown. If the threshold τ ∆ CutPNO is increased, more pairs are treated with smaller PNO domains which leads to reduced timings but increased errors as seen in Fig. ). E.g., for τ ∆ CutPNO = 1 • 10 -3 , the MAD is about 0.47 kJ • mol -1 and the calculations take on average 89% of the time with respect to NORMALPNO DLPNO-CCSD(T 0 ). Increasing the threshold τ ∆ CutPairs reduces the number of orbital pairs included in the amplitude optimizations, as an orbital pair with a relative change below τ ∆ CutPairs is less likely to be considered as strong pair due to the higher pair cutoff. Additionally, the number of triples is influenced as described in Sec. an estimated relative change below 1 • 10 -5 are described with τ CutPNO = 1 • 10 -6 and τ CutPairs = 1 • 10 -3 as for LOOSEPNO since beneficial error cancellation is expected if orbital pairs excluded from the amplitude optimizations and thus described with SC-MP2 are calculated with the same PNO truncation threshold as used for the prescreening procedure (LOOSEPNO SC-MP2). The performance of different threshold combinations for the target accuracy of TIGHTPNO is shown in Tab. SIX of the Supporting Information.