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

The surface chemistry of rutile TiO2(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 TiO2(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 Tint. We found that these excess electrons form polarons and that the most stable structure had one polaron located at the T-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 TiO2(110).