In the intermediate-cost group, M 3,3 and M 4,2 are very similar in terms of their computational cost and performance. Their training set RMSEs of 0.11 eV and 0.12 eV, respectively, are significantly lower than the lower-cost models and their validation set RMSEs of 0.23 eV and 0.22 eV, respectively, are somewhat lower than that of M 1,3 :