The submission AC3 only included entries for FAH, THF, THT and TFE. The conformers of these four systems were found using CREST at GFN2-xTB level of theory. The resulting lowest-energy conformers were then optimized using at B2PLYP-D3(BJ) level of theory with the aug-cc-pvtz basis set and harmonic vibrational frequency calculations were carried out. On paper, this was perhaps the highest-level method for the underlying PES. The same level of theory was then used for a VPT2 treatment of some selected modes that showed a significant contribution from the OH stretch. Preliminary calculations on the acetone-water test system showed significant improvement in the accuracy of the downshift ( by 10 cm -1 with respect to experiments) when nine modes were selected instead of three. The previously mentioned modes were the ones that specifically involved the OH stretch. AC3 therefore chose an anharmonic treatment of nine selected vibrational modes throughout.