These L-VSCF/L-VCI calculations provided anharmonic vibrational frequencies and transition dipole moments for singly and doubly excited states, which could then be used as input for the calculation of the 2D IR spectra. Alternatively, parameters for the construction of a vibrational exciton model as described in Section 2.3 were extracted from the harmonic calculation and the localization as well as the L-VSCF calculation. We considered two different exciton models, termed L-VSCF exciton model and ∆-exciton model.