In general, the GNN predicts the ATCs above the value of about 0.1q well (where q is the electron charge). This is important, because these large ATC values are more likely to dominate the summation in Equation (1), and hence determine the overall magnitude of the exciton coupling. For ATCs below the value of about 0.1q, the GNN's overall accuracy remains high however a larger number of discrepant predictions arise. At this stage it is difficult to explain why discrepancies arise primarily in this range. We will return to this point in the discussion section.