Another approach to compute excitation energies in extended systems using linearresponse DFT is as poles of the imaginary part of the dielectric function (equivalent to the poles of the electric dipole-electric dipole polarizability tensor). More recently, this approach was extended to include band intensities. Equivalently, one can solve the Bethe-Salpeter equation on top of the GW approximation to evaluate the dielectric function. In this case, excitation energies are obtained indirectly by scanning a frequency region to find the poles of the polarizability tensor. To obtain the ECD spectrum, one would need the appropriate combination of the polarizabilities for optical activity (electric dipole-magnetic dipole and electric dipole-magnetic quadrupole). Similarly, the ECD spectrum could be obtained from the ORD curve via a KK transformation, see Eq. 10, which is obtained from the real part of the same optical activity tensors. However, the OR tensor for PBC methods would need to be extended to accommodate a lifetime parameter. Finding the poles of a response function by scanning a frequency range rather than calculating the excitation energies directly would circumvent the need for a TDDFT-PBC implementation, but its applicability seems cumbersome. In fact, one would need to repeat the OR calculation at many frequencies, with tighter grids around the poles' regions, to obtain a reasonable discretization of the dielectric function or of the KK integrals.