For this model dipeptide, we consider 25 structures (with ϕ = -100 • , . . . , -60 • and ψ = -40 • , . . . , 0 • ) in the α-helix region of the Ramachandran plot and 25 structures (with ϕ = -140 • , . . . , -100 • and ψ = +120 • , . . . , +160 • ) in the β-strand region (see Fig. ). For these we performed harmonic calculations of the infrared spectra, from which we extracted the four relevant normal modes. For these, we localized the normal modes, which results in localized modes that describe the two local amide III vibrations (localized modes 3 and 4) and the two pure C α -H bending vibrations 60 (localized modes 1 and 2). These localized modes served as basis for calculations of the anharmonic one-and two-dimensional infrared spectra with localized-mode vibrational self-consistent field (L-VSCF) and localized-mode vibrational configuration interaction (L-VCI), using anharmonic one-mode potentials and harmonic two-mode potentials. Further details are given in the Computational Details below and in the Supporting Information (see Section S1).