Because the nomenclature d - e-h more clearly identifies the physical meaning of this quantity, we prefer that notation over D CT . In any case, this metric is increasingly being used to analyze TD-DFT calculations, though most authors simply refer to it as "D CT ", "Ciofini's CT metric", or similar language that obscures its very straightforward physical interpretation as the distance between barycenters of the particle and the hole. Although this fact has been noted elsewhere, failure to introduce particle and hole densities per se obscures the conceptual origin of D CT and its connection to quantities such as the attachment and detachment densities. For this reason, we suggest that this quantity be called d - e-h rather than D CT , as the physics is inherent in that nomenclature, namely, electron-hole separation as defined by the difference between centroids, rather than the more generic "CT". The definition of d - e-h in Eq. (5.13) is more obvious and meaningful. Even more complicated variants of D CT have been suggested, though it is not clear what advantages these may have as compared to a simple moment analysis of the excitonic wave function, à la Eq. (5.11).