Liquid polyamorphism and double criticality in a lattice gas model

Abstract

We analyse the possible phase diagrams of a simple model for an associating liquid proposed previously. Our two-dimensional lattice model combines orientational ice-like interactions and `van der Waals' interactions which may be repulsive, and in this case represent a penalty for distortion of hydrogen bonds in the presence of extra molecules. These interactions can be interpreted in terms of two competing distances, but not necessarily soft-core. We present mean-field calculations and an exhaustive simulation study for different parameters which represent the relative strength of the bonding interaction to the energy penalty for its distortion. As this ratio decreases, a smooth disappearance of the double criticality occurs. Possible connections to liquid–liquid transitions of molecular liquids are suggested.

Acknowledgement

This work was supported by the Brazilian science agencies CNPq, FINEP, Fapesp and Fapergs.