It is clear from the results in Section 4 .2 that the largest variations amongst basis sets occur for hydrogen-bonded complexes, suggesting that the induction energy is more sensitive to the choice of basis set as compared to other energy components. To investigate this further, we next examine how individual energy components converge with respect to basis set. We do this first for the S66 systems that were examined above (in Section 4 .3 .1) and then for the S22 data set 87 (Section 4 .3 .2). For the latter, high-level SAPT benchmarks are available 88 so we can examine not just convergence but also errors in each energy component.