Whereas the DC-DFT procedure affords a welllocalized hole, with a single spin charge of ≈ 1, the BLYP density evaluated at the same geometry re-introduces Many of these same trends will prove to be on display in a second application that we consider, in which an electron-polaron is created by adding an excess electron to anatase TiO 2 . This is an important material in photocatalysis, gas sensing, and solar cells, due to a favorable combination of low cost, good thermal stability, and lack of significant toxicity. Whereas our previous application used a dopant to create a polaron, localized electronic states arising from structural distortion can be formed upon excitation of transition metal oxides at the band gap. Understanding the behavior of polaronic states is crucial in understanding its charge transport and photocatalytic properties in these materials. The degree to which an electron-polaron localizes in anatase TiO 2 has been a subject of debate. Some studies predict delocalization of the excess charge over multiple Ti ions, but others suggest formation of a small, localized ("self-trapped") polaron. Unsurprisingly, semilocal functions overstabilize chargedelocalized structures. This propensity towards delocalization is somewhat reduced through the use of hybrid functionals, or alternatively via DFT+U. However, the use of potentially non-transferrable parameters in these studies (such as the fraction of exact exchange or the Hubbard U parameter) means that some experimental data are needed to determine the correct approach.