Performance comparison for predicting IR spectra of 12 599 PAHs across charge states, evaluated using the EMD error (x-axis, log scale). NN models with two charge-encoding methods, learnable embedding (a) and one-hot encoding (b), are compared against two baselines: an identical NN without charge encoding (c) and a NN trained or tested only on neutral molecules (d). Vertical dashed lines indicate the mean EMD.