Fig. 4.

O₂ adsorption structures and O₂ dynamics calculated by FPMD-DFT. Lowest-energy structural models and time evolution (first 1.0 ps; for later time the results remain unchanged) of selected ionic distances and charge populations during the adsorption of one O₂ on a the (n × 1) and c the (2 × n) surfaces without a vacancy, and on b the (n × 1) and d the (2 × n) surfaces with one V_O (the O atom filling the V_O is highlighted with a dashed yellow circle). Adsorption energies are indicated, and take into account also the V_O formation energy. Green, red, and blue spheres indicate Sr, O, and Ti atoms, respectively. The intact, adsorbed O₂ molecule and the O atoms resulting from its dissociation are depicted in purple. Five- (a, b) and sevenfold (d) coordination polyhedra of Ti are outlined in white. O1 and O2 refer to the oxygen atoms belonging to the O₂ molecule, while Ti–O1 (Ti–O2) is the distance between O1 (O2) and the closest Ti atom in the structure