Spin contamination was checked by looking at the expectation value of the total spin, ⟨𝑆 $ ⟩. Radicals were expected to have an ⟨𝑆 $ ⟩ = 0.75, and a handful of optimizations were discarded where spin contamination resulted in an ⟨𝑆 $ ⟩ > 0.8. Anions and cations were assumed to adopt a closedshell singlet state, with an ⟨𝑆 $ ⟩~0. To improve the consistency of the dataset, open-shell anions and cations with ⟨𝑆 $ ⟩ > 0.25 were removed.