Stability of Excess Electrons Introduced by Ti Interstitial in Rutile TiO2(110) Surface

The surface chemistry of rutile TiO 2 (110) has long been ascribed to surface bridging oxygen vacancies (V O ) and accompanying excess electrons. However, recently there has been debate whether titanium interstitials (Ti int ), a subsurface defect, participates in the surface reactions of TiO 2 (110). We used a combination of ab initio molecular dynamics and static density functional theory calculations to systematically investigate the spatial distribution of excess electrons introduced by Ti int . We found that these excess electrons form polarons and that the most stable structure had one polaron located at the Ti int site, and the other three at second-layer Ti sites below five-coordinate Ti sites. This behavior of Ti int providing excess electrons to the near-surface region is similar to that of V O, which suggests that Ti int may contribute to the surface chemical reactions of TiO 2 (110).