DFT is applied to study the mechanism of oxygen dissociation on the SrO-terminated surfaces of strontium titanate and iron-doped strontium titanate [1]. Our study reveals that while O2 dissociation is not favored on the SrO-terminated perovskite surface, oxygen vacancies can act as active sites and catalyze the O–O bond cleavage. Electron transfer from lattice oxygen atoms to the O2 molecule, mediated by the subsurface transition metal cations, plays an important role in the resulting formation of surface superoxo species. Our focus on the SrO-terminated surface, rather than the TiO2 layer, which is presumed to be more catalytically active, was driven by experimental observation using low energy ion scattering spectroscopy, which reveals that the surface of SrTiO3 after high temperature heat treatment is SrO-terminated. The interaction of SrO terminated SrTiO3 surface with molecular carbon dioxide and water has been investigated using first-principle theoretical methods and surface analysis techniques. We have studied the formation of a surface SrCO3 layer and various possible products of H2O interaction with the SrO surface, such as, surface chemisorbed water and the formation of a surface hydroxide layer [2]. The co-adsorption of CO2 and H2O was explained both theoretically and experimentally showing that its products follow a complex temperature dependence and as a result, the surface composition may vary between carbonate and surface chemisorbed water. Our theoretical simulations have shown that the presence of water molecules in the gas phase might assist the molecular oxygen/lattice oxygen exchange reaction by stabilization of the surface oxo species in the transition state with a hydrogen bond mechanism. As a result, the activation barrier for molecular oxygen dissociation is decreased leading to an increase in the surface exchange rate constant. Our study demonstrates that the SrO terminated SrTiO3 surface is not static but instead, dynamically responds to external factors such as gas composition, humidity, and temperature. The effect of the partial covalent character of cations on their ionic diffusivity in LSGM is determined computationally [3]. The diffusion of ions is assumed to take place by a vacancy-mediated transport mechanism. Using Vineyard's transition state theory, diffusion coefficients for each ion are obtained. The results of the calculations show that at temperature of 1000 K the diffusivity of the oxide ion is greater than that of the A-site cations by at least ten orders of magnitude, and the diffusivities of the A-site cations are greater then the diffusivities of B-site cations by at least eight orders of magnitude. DFT calculations were performed to elucidate the origin of catalytic activity of the pristine LnO-terminated surfaces of two Ruddlesden–Popper phase oxides of industrial interest [4]. The direct comparison of molecular oxygen interaction with La2NiO4 and Pr2NiO4 allowed us to evaluate the electronic effect on the oxygen reduction reaction energetics. We have further addressed the surface catalytic activity as a function of interstitial oxygen occupancy in the rock salt layer and provided a possible explanation for the limits of the interstitial oxygen concentration. The oxide ion transport in the rock salt layer was compared and the diffusion difference was attributed to the electronic structure of the valence shells of Pr and La. The different polarizability of those elements would lead to the opposite effect on the transition state stability. The high oxide-ion transport in three fluorite-structured oxide electrolytes is examined by using DFT [5]. Our study elucidates the oxide-ion diffusion mechanism in yttrium (Y)-doped ZrO2, Y-doped CeO2, δ-Bi2O3, and α-Bi2O3, including the major change in oxygen mobility that occurs in Bi2O3 at the δ–α phase transition. This research focuses on the partial covalent interactions, often neglected in atomistic simulations, and their effect on the migrating oxygen ion.