Also for IR spectra the agreement was reasonably successful, within the limits of our computational method, which does not include an explicit description of the solvent, beyond a few hydrogen-bonded water molecules. The consideration of different conformers, particularly those deviating from the average stretched conformation of the peptide, was again crucial (Fig. ). The Raman and ROA spectra proved more challenging, due to the higher sensitivity of the methods to the conformational degrees of freedom of the side chains and their solvation states. Regarding the Raman spectrum, the agreement is modestly improved after protonating the imidazole rings of all histidine residues, although such a high protonation state would not be expected under the pH conditions employed in the experiments. This demonstrates how challenging it is to properly model Raman and ROA spectra of peptides as the calculated spectrum is determined by all aspects of the considered model such as the protonation state, the side-chain conformations and dynamics, solvation, etc. The impor-tance of incorporating conformational flexibility was especially clear for the ROA, for which not only the backbone conformation needs to be properly averaged over many conformations, but also many side chain rotamers need to be explicitly included to properly account for their contributions. Possibly, a clustering algorithm including both the backbone and the side-chain degrees of freedom might need to be developed and deployed to predict ROA observables in better agreement with experiments.