Figure shows a Pareto plot of the accuracy vs the computational cost of the SISSO-generated models for the triplet excitation energy. The equations of all the models, as well as tabulated values of their cost and accuracy are provided in the ESI. Similar to the results for the optical gap, the triplet exciton energy models are clustered in three groups of lower, intermediate, and higher computational cost. In contrast to the optical gap models, in this case, the models in the lower-cost group only require the calculation of single molecule primary features, which makes them very cheap to evaluate. The models in the intermediate-cost group are more complex and contain various crystal primary features. The higher- cost group contains the higher complexity fourth rung models, M 4,2 and M 4,3 . These models contain both of the high-cost features ET C and H ab , as well as multiple other primary features, which contribute to their high cost.