where ℑ denotes the imaginary part, and μ and m are the operators of the electric and magnetic moment vectors respectively. Their matrix elements in the exciton basis are obtained by combining the electric (µ ia ) and magnetic (m ia ) transition dipoles of the chromophores. A common approximation is to neglect the intrinsic magnetic dipole moments of the chromophore transitions. However, considering the intrinsic magnetic moments is actually fundamental to describe the n → π * transitions of the peptide bonds, which have a strong magnetic character. Here we employ an origin-invariant expression for the rotational lated and experimental spectra. A similar approach has been successfully employed for the calculation of CD spectra of DNA G-quadruplexes .