Liquid polymorphism, density anomaly and H-bond disruption in an   associating lattice gases
  We have investigated the effects of either distorting hydrogen bonds or removing proton degeneracy on the thermodynamic properties of a minimal model for associating liquids. The presence of two liquid phases and a density anomaly is unaffected in both cases. Increasing the degeneracy of bonded structures leads to lower temperature critical points and a steeper liquid-liquid coexistence line, implying a low density liquid of larger entropy.   Analysis of the hydrogen bond net accross the phase diagram indicates that the density anomaly is accompanied by a steep reduction of hydrogen bond density, which introduces a restriction on a correlation which has been preconized long ago. This feature is present independent of bond distortion or of the presence of proton entropy. 
Aline Balladares, Vera B. Henriques and Marcia C. Barbosa