Strongly non-Arrhenius self-interstitial diffusion in vanadium

We study diffusion of self-interstitial atoms ({SIAs)} in vanadium via molecular-dynamics simulations. The ⟨111⟩-split interstitials are observed to diffuse one-dimensionally at low temperature, but rotate into other ⟨111⟩ directions as the temperature is increased. The {SIA} diffusion is highly non-Arrhenius. At T{\textless}600 K, this behavior arises from temperature-dependent correlations. At T{\textgreater}600 K, the Arrhenius expression for thermally activated diffusion breaks down when the migration barriers become small compared to the thermal energy. This leads to Arrhenius diffusion kinetics at low T and diffusivity proportional to temperature at high T.