Topological and real charge of Bjerrum defects in ices Ih and Ic

Two mechanisms for the interaction of Bjerrum defects in ices are considered. (i) In the lattice ice models, the defects are topological charges interacting by the entropy of proton disorder. The charge magnitude is calculated by fitting the potential of mean force of a pair of defects (minus log of the simulated 3D distribution function) in the periodic boundary conditions to the Ewald summation energy. (ii) At the atomic level, the effective Coulomb charges for several classical water models are calculated as a sum of Gaussian-smoothed partial charges. The topological charge is equivalent to % of the Bjerrum defect real charge. [GRAPHICS] .