The field of geological materials is rapidly opening up to computer modelling and ice poses stimulating new problems. The normal pressure and 0°C form of ice is ice Ih in which the oxygen sublattice is wurtzite. Imagining first that the protons occupy O–O “bond-centre” sites, it is generally believed that in ice Ih these protons are displaced along the bond direction in a correlated fashion such that each oxygen has two close protons (at about 1Å ) and two more distant ones (at about 1.7Å ). The correlated “disorder” of protons causes frustration of certain atomic movements, such as water molecule reorientation (as measured by dielectric relaxation times) and dislocation glide. Frustration can be relieved (and dislocation glide facilitated) by proton order defects, such as ionic defects, like an oxygen surrounded by only one close proton (OH−) or three (H3O+), or Bjerrum defects, like an O–O link with no intervening proton (L defect) or two protons (D defect).

We present results of ab initio total energy calculations on the formation of these defects.