Both of these are similar to a different charge-separation metric (∆σ) introduced by Adamo et al., which will be discussed in Section 6.2. Essentially the same information that is encoded in D CT and ∆σ is contained also in the quantities d - e-h and d CD , but the latter are defined in a manner that is more directly connected to properties of the particle and the hole. This analysis furthermore clarifies why the values of various chargedisplacement metrics are found to be strongly correlated with one another. In this author's view, the use of d - e-h (distance between the centroids of the electron and the hole) and d CD (center-to-center distance reduced by the average of the RMS size of the electron and the hole) are preferable ways to measure exciton size and electron-hole separation. These quantities provide a more intuitive and mutually self-consistent way to convey the same information as the D CT and t indices.