The weighting scheme used is the same as the one used to optimise ωB97M(2). Each data-point in a given dataset is assigned an initial weighting w i = (N i ∆E i ) -1 where N i is the total number of data-points in the dataset, and ∆E i is the root-mean-square of the reaction energies in the dataset i. For each data-type, the weights are then normalised by dividing all values by the minimum initial weight w d min , and exponentiated so that they lie in between 1 and 2. During this calculation the AE18 dataset is included in the TCE data-type.