In ordered systems, such as globular proteins with high amount of β-sheets and α-helices, the microstates composing the conformational ensemble can be clustered together into one or just a few well-defined structures. From a theoretical point of view, predicting these structures by global minimization of the system's free energy landscape is very demanding for proteins, but possible for short peptides with around 10 amino acids, via enhanced sampling methods. A further difficulty is the theoretical calculation of their optical or vibrational spectra. Their intrinsic order requires very accurate consideration of the coupling between the amide chromophore units along the protein backbone with the (flexible but constrained) side-chains and the surrounding solvent. In principle, theoretical spectra can be computed with ab-initio methods, posing however a severe limit to the manageable system size, which should not exceed a few thousands atoms.