Different water scenarios for a primitive model with two types of hydrogen bonds

Using a primitive water model, we find that the strength of tetrahedral interactions can change the behavior of liquid water from the liquid-liquid critical point scenario to the singularity-free scenario. Specifically, we find that the strongly tetrahedral model has a liquid-liquid critical point from which the Widom line emanates with a negative slope, but that the weakly tetrahedral model lacks the second critical point and the line of the specific heat maxima analogous to the Widom line has a positive slope. The strongly tetrahedral interaction is characterized by a double-step potential that depends on hydrogen-bond bending, while the weakly tetrahedral interaction has a uniform single-step potential. Copyright (C) EPLA, 2012