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| - On the Trapping of Bjerrum Defects in Ice Ih: The Case of the Molecular Vacancy
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| Abstract
| - We present a density-function theory (DFT) study of Bjerrum-defect trapping centers involving the molecularvacancy in ice Ih. As a first step, we compute the intrinsic migration barrier to D-defect motion using thenudged elastic band (NEB) method and find them to be of the same order of magnitude as the energy barriersinvolving intrinsic L-defect motion. This finding suggests that intrinsic mobility factors cannot explain theexperimentally 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 witha molecular vacancy. The corresponding geometries show that the formation of these aggregates significantlyreduces elastic distortions that are present in isolated Bjerrum defects. An analysis of the energetics involvedin the formation of both defect complexes reveals a significant binding energy, indicating that the molecularvacancy represents a strong trapping center for Bjerrum defects. On the other hand, the fact that there is nodifference between the absolute values of the binding energies for both D and L defects suggests that thevacancy affects both species of Bjerrum defects in a similar fashion, possibly ruling out the vacancy trappingcenters as an explanation for the experimentally observed inactivity of D defects.
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