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Ab initio electronic structure calculations are employed to study the stability and mobility of mono-self interstitial atoms ͑SIA͒ in ␣-Fe under external deformation. The ab initio results indicate that the volumetric and uniaxial strain dependences of the SIA formation energy are different in the expansion and compression regimes, in contrast to the linear behavior in continuum elasticity theory. We find a ͗111͘ → ͗100͘ SIA reorientation mechanism induced by uniaxial expansion which proceeds via ͗11x͉͘ x=2.7 configuration. Volumetric and uniaxial deformations are also found to have a considerable influence on the migration paths and activation energy barriers for the ͗110͕͘110͖ ↔ ͗100͕͘100͖ transformation and the ͗111͘ ↔ ͗100͘ reorientation. The results reveal that ͑i͒ the volumetric expansion ͑compression͒ decreases ͑increases͒ substantially the migration energy barrier and renders the diffusion process three ͑one͒ dimensional, ͑ii͒ the uniaxial strain removes ͑decreases͒ the migration energy barrier for the ͗111͘ → ͗11x͉͘ x=2.7 ͑͗11x͉͘ x=2.7 → ͗100͒͘ transformation, leading to spontaneous reorientation of the ͗111͘ SIA, and ͑iii͒ the uniaxial deformation breaks the cubic symmetry of the system and in turn induces anisotropy of the migration rates along different directions. These calculations demonstrate that changes in the electronic structure induced by global elastic deformation lead to additional contributions to the formation and migration energies, which cannot be adequately accounted for neither by elasticity theory nor by empirical interatomic potentials.

The stress fields of dislocations predicted by classical elasticity are known to be unrealistically large approaching the dislocation core, due to the singular nature of the theory. While in many cases this is remedied with the approximation of an effective core radius, inside which ad hoc regularizations are implemented, such approximations lead to a compromise in the accuracy of the calculations. In this work, an anisotropic non-singular elastic representation of dislocation fields is developed to accurately represent the near-core stresses of dislocations in α-iron. The regularized stress field is enabled through the use of a non-singular Green's tensor function of Helmholtztype gradient anisotropic elasticity, which requires only a single characteristic length parameter in addition to the material's elastic constants. Using a novel magnetic bond-order potential to model atomic interactions in iron, molecular statics calculations are performed, and an optimization procedure is developed to extract the required length parameter. Results show the method can accurately replicate the magnitude and decay of the near-core dislocation stresses even for atoms belonging to the core itself. Comparisons with the singular isotropic and anisotropic theories show the non-singular anisotropic theory leads to a substantially more accurate representation of the stresses of both screw and edge dislocations near the core, in some cases showing improvements in accuracy of up to an order of magnitude. The spatial extent of the region in which the singular and non-singular stress differ substantially is also discussed. The general procedure we describe may in principle be applied to accurately model the near-core dislocation stresses of any arbitrarily shaped dislocation in anisotropic cubic media.

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