Adsorption of atomic and molecular oxygen on the SrTiO₃(001) surfaces: Predictions by means of hybrid density functional calculations

Ab initio calculations based on density functional theory (DFT) were used to study the energetics, geometry of fully relaxed structure, and electronic charge redistribution for adsorbed atomic and molecular oxygen on defectless unreconstructed SrTiO₃(001) surfaces, both SrO- and TiO ₂-terminated, B3PW functional used in our calculations contains a "hybrid" of the DFT exchange and correlation functionals with exact non-local Hartree-Fock (HF) exchange. We performed calculations of two-dimensional slabs with unit cells large enough for the adsorbed species to be treated as isolated. We found substantial binding energies for atomic O adsorption at bridge positions between the two adjacent metal and oxygen surface ions (much closer to the latter) on both SrO- and TiO₂-terminated surface (over 2.0 eV with respect to free atom). In both cases strong bonding is rather caused by formation of surface molecular peroxide ion in singlet state. For molecular adsorption, different adsorption sites and orientations of OT molecule were studied, however, adsorption energy never exceeded 0.1 eV. However, energy gain obtained from adsorption of atomic oxygen is not sufficient for molecule dissociation.