Percolating networks and liquid-liquid transitions in supercooled water

The anomalous behaviour of various properties of liquid water upon cooling may be explained by approaching the percolation transition of the four-coordinated water molecules or by approaching the liquid-liquid transition. We have found these two explanations are intrinsically closely related by locating the line of the percolation transitions of the four-coordinated water molecules with respect to the liquid-vapour and liquid-liquid transitions of ST2 water. The saturated liquid water upon cooling crosses the percolation threshold of the four-coordinated water molecules, which is close to the binodal (spinodal) of the first (lowest-density) liquid-liquid transition of water. This finding agrees with the known close relation between the phase transition and the percolation transition of physical clusters. The lowest-density amorphous water phase is characterized by presence of a percolating network of the four-coordinated water molecules. The line of the percolation transitions of tetrahedrally ordered water molecules ( with arbitrary coordination number) envelops the whole region where liquid liquid transitions occur. So, the percolating network of the tetrahedrally ordered water molecules is absent in the highest-density amorphous water phase.