Effect of lattice coarsening and exclusion on phase-transition properties of the Bell–Lavis model

Abstract

The temperature and order of the phase transition are studied for a less-coarsened Bell–Lavis model. The interactions exist between triangular molecules being on third-neighbour (3NN) sites, while the nearest-neighbour (1NN) interactions are subject to a hard core exclusion. Using Monte Carlo calculations, we obtain the temperature, and chemical potential phase diagram for a whole range of values, where the honeycomb phase exists. We find that the entropy gain prevails at low molecular densities (high ). Therefore, the first-order disordered-to-honeycomb phase transition found in the 3NN model has lower temperature than that of the 1NN model. At higher molecular densities (low ), below the tricritical point, the exclusions start to play some role and the entropy decreases. This leads to the occurrence of the intermediate short-range ordered phase in between disordered and honeycomb phases. The upper phase transition is found at higher temperature, while the lower one at the same temperature as that of the 1NN model. The critical exponents obtained for the lower phase transition demonstrate the values typical for the three-state Potts model universality class.