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Using nonequilibrium molecular dynamics simulations, we investigate the process of grain-boundary (GB) sliding in ice Ih. We focus on the ∑35 symmetric tilt boundary, which has been observed experi...

We investigate the uptake of HCl and HF at lattice vacancies in ice Ih as a function of their distance to the basal-plane surface layer using density-functional theory calculations. The results for HCl display large dispersions in the binding-energy results due to the appearance of distinct dissociation states. The layer-averaged results suggest that the uptake of HCl is most favorable in the two layers just below the surface, which is consistent with available experimental indications. The behavior of HF is found to be manifestly different due to the fact that it is a weaker acid. The dispersion in the binding-energy values is significantly less compared to the case of HCl, and the average values are essentially equal to the bulk value, regardless of layer position. This suggests that, in contrast to the case of HCl, there should not be any tendency for accumulation of HF near the surface.

We present a density-function theory (DFT) study of Bjerrum-defect trapping centers involving the molecular vacancy in ice Ih. As a first step, we compute the intrinsic migration barrier to D-defect motion using the nudged elastic band (NEB) method and find them to be of the same order of magnitude as the energy barriers involving intrinsic L-defect motion. This finding suggests that intrinsic mobility factors cannot explain the experimentally observed inactivity of D defects, supporting the idea that D defects are trapped at other lattice-defect sites. Next we study the defect complexes formed by the combination of isolated D and L defects with a molecular vacancy. The corresponding geometries show that the formation of these aggregates significantly reduces elastic distortions that are present in isolated Bjerrum defects. An analysis of the energetics involved in the formation of both defect complexes reveals a significant binding energy, indicating that the molecular vacancy represents a strong trapping center for Bjerrum defects. On the other hand, the fact that there is no difference between the absolute values of the binding energies for both D and L defects suggests that the vacancy affects both species of Bjerrum defects in a similar fashion, possibly ruling out the vacancy trapping centers as an explanation for the experimentally observed inactivity of D defects.