Order-disorder transition in a two-dimensional associating lattice gas

Area of Science:

• Statistical Mechanics
• Condensed Matter Physics

Background:

• The associating lattice gas (ALG) model simulates molecules with orientational degrees of freedom, mimicking hydrogen bond formation.
• Previous studies have not systematically investigated the transition between the high-density liquid (HDL) and isotropic phases at full occupancy (chemical potential μ→∞).

Purpose of the Study:

• To systematically study the phase transition between the HDL and isotropic phases in the ALG model at full occupancy.
• To determine the universality class of this phase transition and compare simulation results with theoretical models.

Main Methods:

• Monte Carlo simulations were performed on a triangular lattice.
• Semianalytical solutions were obtained using Husimi lattices.

Main Results:

• Simulations revealed a continuous phase transition at τ_{c}=0.4763(1), with critical exponents and Binder cumulant indicating the three-state Potts model universality class.
• Husimi lattice analyses predicted a discontinuous phase transition with slightly higher transition temperatures.
• Discrepancies suggest three possible scenarios for the triangular lattice's phase diagram at full occupancy.

Conclusions:

• The study highlights a potential discrepancy between simulation and theoretical models for the ALG phase transition.
• The findings suggest that the transition might belong to the three-state Potts model universality class, even without full symmetry.
• Further investigation is needed to resolve the differing predictions for the phase diagram at full occupancy.