Within the framework of density functional theory, using the projector augmented-wave method, energetic properties of atomic O interstitials in crystalline Ni were deduced. With regard to the activation energy, 2 pathways for migration were studied. The charge-transfer process between atomic O and Ni atoms was analyzed for interstitial sites. It was found that the interstitial octahedral site (O-site) was lower in energy than was the tetrahedral site (T-site). The most favourable pathway for migration between 2 octahedral sites corresponded to an intermediate metastable state located in a tetrahedral site. With regard to charge transfer, it was found that the atomic O ionized to O- and that the electron essentially migrated from the Ni nearest-neighbours of atomic O. A thermal-expansion contribution arising from dilatation of the solid was also studied. When thermal expansion was introduced, it was found that the insertion process was stabilized and that the tetrahedral insertion energy became almost equal to the octahedral one. However, the activation energy decreased with dilatation. Taking account of the thermal expansion effects, the results were consistent with the more reliable experimental data.First-Principles Calculations of the Diffusion of Atomic Oxygen in Nickel - Thermal Expansion Contribution. E.H.Megchiche, M.Amarouche, C.Mijoule: Journal of Physics - Condensed Matter, 2007, 19[29], 296201 (8pp)