Extended lattice model of water; Two-sublattice, two-orientation model

The phase diagram obtained by a simple H-bonded lattice model for water is extended in order to describe this diagram in more detail by introducing two additional degrees of freedom: the sublattice occupation and the orientation. The resulting phase diagram has four different regions associated with: vapor, open ice, water and a general form of close packed ice. The open to close-packed transition is a second order transition. The density as a function of the temperature at a pressure below the critical point and above the triple point is given. It shows the behavior characteristic of water; a liquid-density in excess of the solid density. We obtained the fraction of broken hydrogen-bonds as a function of the temperature at the same pressure. Finally the behavior of the metastable stay states is given for the various transitions. These extensions of the phase line lead to additional end points and triple points.