Grain boundary diffusion in Yukawa crystals.

We present calculations of diffusion coefficients in grain boundaries (GBs) in Yukawa crystals for astrophysics. Our methods follow from our recent work calculating diffusion coefficients in perfect body-centered cubic crystals. These diffusion coefficients show only a weak dependence on the crystal orientations at the GB and are consistent with those expected for a supercooled liquid scaled down by 1-2 orders of magnitude. We argue that the local disorder at the GB produces a landscape of potential barriers similar to that of an amorphous liquid thin film, significantly reducing activation barriers to diffusive hops relative to the bulk solid. This also introduces a screening dependence, such that boundary diffusion does not exhibit the same universality as the bulk crystal. These diffusion coefficients suggest that GBs may be a dominant source of plastic dissipation in neutron star crusts.