An off-lattice, on-the-fly kinetic Monte Carlo model was presented for simulating stress-assisted diffusion and trapping of hydrogen by crystalline defects in iron. Given an embedded atom potential as input, the energy barriers to diffusion were ascertained on the fly from the local environments of H atoms. In order to reduce computational cost, on-the-fly calculations were supplemented with pre-computed strain-dependent energy barriers in defect-free parts of the crystal. These pre-computed barriers, obtained from high-accuracy density functional theory calculations, were used to ascertain the accuracy of the embedded atom barriers and to correct them when necessary. Examples of bulk diffusion in crystals containing a screw dipole and vacancies were presented. The effective diffusivities obtained from kinetic Monte Carlo simulations were found to be in good agreement with theory. The model provided a route for simulating the interaction of hydrogen with cracks, dislocations, grain boundaries, and other lattice defects, over extended time scales, albeit at atomistic length-scales.

Effect of Atomic Scale Plasticity on Hydrogen Diffusion in Iron - Quantum Mechanically Informed and On-the-Fly Kinetic Monte Carlo Simulations. A.Ramasubramaniam, M.Itakura, M.Ortiz, E.A.Carter: Journal of Materials Research, 2008, 23[10], 2757-73