We have shown that experimental CD spectra of ordered peptides and proteins can be well reproduced by the average of the computed CD spectra for all conformers in the ensemble, employing semi-empirical methods, e.g. with the DichroCalc server. In this study, we deploy a novel, more accurate but computationally more demanding, method for the calculation of CD spectra for disordered ensembles (cf. ESI for computa-tional details). The approach is based on an excitonic model developed previously to predict optical spectra of multichromophoric systems, and applied to biopolymers and pigmentprotein complexes. In this model, the properties of the single chromophoric units (here the peptide bonds, modelled as an N-methyl acetamide (NMA) fragments) are combined together to describe the excited states of the entire system. Each peptide bond is modeled in an idealized planar geometry and computed in the polarizable MM (MMPol) environment of the rest of the system. In this way, the resulting CD spectra depend both on the arrangement of the NMA chromophores (i.e. on the peptide's secondary structure) and on other effects captured by the MM embedding, such as the conformation of the side chains and the arrangement of the solvent around the backbone.