If one removes some of the polarization functions from the highest-quality Pople basis set, to obtain 6-311+G(2df,2p), the speedup relative to def2-TZVPD increases to 5× while preserving the accuracy of E int , at the expense of introducing a small amount of error can-cellation between E elst and E ind . This basis is superior to def2-SVPD in both accuracy and efficiency. Nevertheless, it is worth noting that the error in the 6-31+G(d) calculations appears to be quite systematic while affording a speedup of 37× relative to def2-TZVPD. The more affordable Pople basis sets therefore offer good insight as to how the energy components change as a function of geometry in large systems. 60 4.5.2. Basis-Set Convergence for F -(H 2 O) 6 . In a similar vein, we next examine energy components for F -(H 2 O) 6 , for which CCSD(T)/CBS benchmarks 97 allow us to characterize absolute errors in the interaction energies. In contrast to the Cl -(aq) system, where each Cl -(H 2 O) n cluster was treated as a dimer, here we exploit the many-body power of XSAPT to describe F -(H 2 O) 6 as a system of 7 fragments.