Fig. 1.

Adsorbed molecular ${\mathrm{O}}_2$ and atomic O. (A and B) Constant-height AFM images obtained after ${\mathrm{O}}_2$ dosing at 10 K and 80 K, respectively, showing adsorbed molecular ${\mathrm{O}}_2$ (circles) and atomic O species (squares). (C) DFT calculation of the polaronic ground state of the clean, reduced surface with one bridging-oxygen vacancy. (Left) The total DOS (black) and the partial contributions of the adsorbed O atoms (red) and their nearest Ti atoms (blue). The in-gap state is magnified in Inset. (Right) Partial charge-density plots showing the top and the side view of the charge distribution of the two excess electrons originating from the ${\mathrm{V}}_{\mathrm{O}}$. (D–G) DFT calculations of the molecular ${\mathrm{O}}_2$ (D–F) and atomic O (G) adsorption configurations marked in constant-height AFM images, together with their respective names in the nomenclature adopted throughout this paper. (H) Table summarizing the adsorption energy $E_{\mathrm{a}\mathrm{d}\mathrm{s}}$ and spin states of the adsorbates; O–O bond lengths $d$(${\mathrm{O}}_2$) and Bader charges $Q_{\mathrm{B}}$ of the $\tau$, $\pi$, and $\omega$ molecules; and the Bader charge $Q_{\mathrm{B}}$ of the oxygen adatom ${\mathrm{O}}_{\mathrm{a}\mathrm{d}}$.