For the calculation of 2D-IR spectra, we employed the methodology previously established in Ref. 59. Briefly, the extended amide III modes were localized using our LocVib Python package, resulting in localized-mode coordinates, localized-mode harmonic frequencies, transition dipole moments, and harmonic coupling constants. Within these localized-mode coordinates, anharmonic one-mode potentials were calculated using Turbomole/BP86/def2-TZVP, and anharmonic frequencies and transition dipole moments were calculated with L-VSCF/L-VCI including single and double excitations (L-VCISD) using our Vibrations code. These anharmonic frequencies and transition dipole moments were used as input for the calculation of 2D-IR spectra as described in Ref. 59. The dephasing time was set to T 2 = 1 ps, the time delay between the laser pulses was set to t 2 = 0 ps, and the polarization condition was set to ⟨ZZZZ⟩. Results for ⟨ZZXX⟩ and ⟨ZXXZ⟩ polarization conditions are shown in figures S13 and S14. Further details on the computational methodology are provided in Section S1 of the Supporting Information. All plots of spectra were prepared using Matplotlib.