Phase diagram of a double-occupancy cell model of a fluid with Curie-Weiss interaction
DOI:
https://doi.org/10.5488/cmp.29.33603Keywords:
double-occupancy cell model, Blume-Capel model, liquid-liquid phase transition, liquid-liquid critical pointAbstract
A double-occupancy cell model of a fluid with Curie-Weiss interaction is studied. First, we show that the model is isomorphic to the Blume-Capel model on a complete graph through a simple transformation from spin to occupancy variables. We then investigate its phase behavior within the grand-canonical ensemble using a combination of analytical and numerical methods. Despite its simplicity, the model exhibits a remarkably rich thermodynamic behavior depending on the ratio between the local repulsive and global attractive interactions. We identify the regimes characterized by a single critical point, two distinct critical points, tricritical behavior, and triple-point formation. For sufficiently strong repulsion, the system possesses three fluid phases of different densities, leading to both gas-liquid and liquid-liquid coexistence. The locations of the critical, tricritical, and triple points are determined, and the corresponding phase diagrams are constructed. These results demonstrate that the competition between double-occupancy repulsion and long-range attraction is sufficient to generate a complex phase behavior in a minimal multiple-occupancy lattice-gas-like model.
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