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|Type:||Artigo de periódico|
|Title:||Structure and energetics of extended defects in ice I-h|
de Koning, M
|Abstract:||We consider the molecular structure and energetics of extended defects in proton-disordered hexagonal ice I-h. Using plane-wave density functional theory (DFT) calculations, we compute the energetics of stacking faults and determine the structure of the 30 degrees and 90 degrees partial dislocations on the basal plane. Consistent with experimental data, the formation energies of all fully reconstructed stacking faults are found to be very low. This is consistent with the idea that basal-plane glide dislocations in ice I-h are dissociated into partial dislocations separated by an area of stacking fault. For both types of partial dislocation we find a strong tendency toward core reconstruction through pairwise hydrogen-bond reformation. In the case of the 30 degrees dislocation, the pairwise hydrogen-bond formation leads to a period-doubling core structure equivalent to that seen in zinc-blende semiconductor crystals. For the 90 degrees partial we consider two possible core reconstructions, one in which the periodicity of the structure along the core remains unaltered and another in which it is doubled. The latter is preferred, although the energy difference between both is rather small, so that a coexistence of both reconstructions appears plausible. Our results imply that a mobility theory for dislocations on the basal plane in ice I-h should be based on the idea of reconstructed partial dislocations.|
|Editor:||Amer Physical Soc|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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