where ŷi is the DFT ATC value for atom i. Equation ( ) was summed over all molecules in the validation set. The minimization was performed using the Adam optimizer, using an initial learning rate of 0.001 and a batch size of 128. The GNN terminated if the loss function showed no improvement after 50 successive learning steps. We stress that our GNN is only able to predict the magnitude of the ATC value and not its phase (sign). This will become a problem when using Equation (1) to compute the coupling, as the sign of the ATC matters in the calculation. In this work, we use the GNN to predict ATC magnitude and assigned its phase on the basis of a DFT calculation. This is only a mild shortcoming of our framework, as it turns out that ATC phase can be obtained quite quickly using very low-cost functionals and basis sets, and by terminating the DFT selfconsistent loop long before convergence. We will return to this point in the discussion section.