Orientational Defects in Ice Ih: An Interpretation of Electrical   Conductivity Measurements
  We present a first-principles study of the structure and energetics of Bjerrum defects in ice Ih and compare the results to experimental electrical conductivity data. While the DFT result for the activation energy is in good agreement with experiment, we find that its two components have quite different values. Aside from providing new insight into the fundamental parameters of the microscopic electrical theory of ice, our results suggest the activity of traps in doped ice in the temperature regime typically assumed to be controlled by the free migration of L defects. 
Maurice de Koning, Alex Antonelli, Antonio J. R. da Silva and A.   Fazzio