Skin O:H–O segmental length and stiffness cooperative relaxation.^[53] Length and stiffness (inset) transition for the (a) H–O bond and (b) O:H nonbond from the bulk value (b) to the skin (s) and to the H–O free radicals (r). Inset (a) shows the complex unit cell denoted with bulk, skin, and a vacuum slab. The P components arise from the screening and splitting of the crystal potentials by polarization.