As discussed in Section 5, exciton size and delocalization can be characterized and quantified using properties of the transition density T (r elec , r hole ), providing access to correlations between the electron and the hole quasiparticles that cannot always be inferred from the MOs and excitation amplitudes alone. This has a bearing on diagnosing anomalous CT in TD-DFT calculations, as shown schematically in Fig. using ladder-type poly(p-phenylene) polymers as an example. Here, TD-DFT calculations using semilocal functionals (GGAs) predict a bound exciton that is delocalized across the entire polymer, regardless of oligomer length, which is the same problem that was documented for (PPV) 20 in Fig. . In the latter case, hybrid functionals with a large fraction of Hartree-Fock exchange significantly attenuate the charge separation (although not the FE delocalization). As indicated in Fig. , LRC functionals also predict a finite size limit, in agreement with many-body calculations. Such functionals include 100% Hartree-Fock exchange at long range only. The DMABN molecule that was introduced in Section 4.3 provides an interesting case study in TD-DFT's description of CT, and Fig. characterizes the nature of its S 0 → S 1 and S 0 → S 2 transitions using particle and hole densities. These are the 1 L a and 1 L b states, and according to the lore one of them should be the 1 ππ * or "LE" state, while the other should exhibit nascent CT character that is enhanced upon twisting. At the planar ground-state geometry (on the left in Fig. ), both transitions exhibit significant delocalization across the donor-π-acceptor framework, although the excited electron (attachment density) has slightly more density on the cyano group in S 2 than in S 1 . Introducing a 90 • twist of the amino group (on the right in Fig. ), and in a dielectric medium characteristic of acetonitrile, detachment densities for both transitions localize on the n(NH 2 ) lone pair. For the twisted geometry, S 1 is clearly the CT state and it is significantly stabilized by solvent polarization. In contrast, the excitation energy for the LE state is scarcely affected by the twist.