(a) A dense tetrahedral cluster in MD model of liquid water at 300 K and its frame (broken red line); blue points are the molecules and red points are centres of the cluster tetrahedrons; (b) the helical atomic model for this cluster with possible coherent exchange of protons (red balls) between oxygen atoms (blue balls) along the helix of hydrogen bonds (black lines) and hydrogen-bond bridges (pink balls); the projections of oxygen atoms in the plane are denoted by numbers.
