Phenomenological damping in optical response tensors

Although perturbation theory applied to the optical response of a molecule or material system is only strictly valid far from resonances, it is often applied to ‘‘near-resonance’’ conditions by means of complex energies incorporating damping. Inconsistent signs of the damping in optical response tensors have appeared in the recent literature, as have errors in the treatment of the perturbation by a static field. The ‘‘equal-sign’’ convention used in a recent publication yields an unphysical material response, and Koroteev’s intimation that linear electro-optical circular dichroism may exist in an optically active liquid under resonance conditions is also flawed. We show that the isotropic part of the Pockels tensor vanishes.