Spin-orbit coupling (SOC) stabilization energy has previously been shown by Khanniche et al. to be significant for the low-energy isomer of iodous acid: HOIO. Likewise they showed that it should be neglible for the low-energy isomer of iodic acid: HOIO 2 . The methods employed by Khanniche et al., CASSCF-CASPT2 with SOC via SO-RASSI with the ANORCC-VQZP basis set on B3LYP/aug-cc-pVTZ-PP structures, are too expensive for extensive calculations, therefore we attempt to approximate the results with TD-DFT. As the reference results are calculated on a structure optimized at a different level of theory, we tested the sensitivity of the TD-DFT calculated SOC to the structure in Figures S4 and S5 in Section S2.2 of the SI. We found that it is very insensitive to the applied method and size of basis set. The primary factor deciding the magnitude of the calculated SOC stabilization energy is therefore the number of states included in the calculation.