Hyperparameter values were initially selected to give an even spacing of Gaussians out to the largest intermolecular nearest atom-atom distance for radial terms, and to sample -π to π for the angular terms. The number of symmetry functions and hyperparameters were then optimized using the the entire dataset of both species at the FIT+DMA level of theory, where the number of symmetry functions was reduced to the minimum number at which all dimers were fully distinguishable with nearby neighbours in descriptor space displaying similar FIT+DMA dimer energies. Three radial and two angular terms were used to describe each atom in the oxalic acid and maleic hydrazide dimers (giving a total of 80 symmetry functions per oxalic acid dimer and 120 symmetry functions per maleic hydrazide dimer).