Abstract <p>Diffusion of oxygen and nitrogen in titanium nitride was studied using the projector augmented wave method in combination with transition state theory. Atomic migration energies were calculated for two diffusion mechanisms (interstitial and vacancy ones). It was found that the oxygen migration energy by the interstitial mechanism is ~0.3 eV lower than that by the nitrogen vacancy mechanism. However, the indirect mechanism of diffusion through the body-centered position of the cubic lattice formed of titanium and nitrogen atoms is more preferable. The estimation of the temperature-dependent coefficient of oxygen and nitrogen diffusion in titanium nitride by the two mechanisms showed their strong dependence on the concentration of thermal vacancies. It was shown that the interstitial diffusion of nitrogen occurs at temperatures below 1500°C, and the vacancy diffusion mechanism prevails at high temperatures. The calculated activation energies and diffusion coefficients showed good agreement with the experimental values. At high concentrations of constitutional vacancies, the coefficients of oxygen diffusion by both mechanisms are comparable with the experimental values for TiO₂, and the values obtained at low concentrations remain several orders of magnitude higher than those for Al₂O₃.</p>