Spin-One Lattice-Gas Model

Abstract

Many cooperative systems are characterized by a single order parameter and a second order phase transition at a critical point. Their thermodynamical behaviour can be simulated by a spin half Ising model with positive dipolar interactions. For instance [1]:

• magnetic ordering in a uniaxial or isotropic system;

• phase separation in a binary mixture;

• condensation of a simple fluid (Lee and Yang);

• freezing of a liquid (Lennard-Jones and Devonshire);

• suprafluid ordering (London, Tisza [2]);

• magnetic ordering in a two-singlet system (Bleaney, Cooper);

• ferroelectric ordering in KDP (De Gennes);

• ordering in molecular crystals: NH₄Cl, NaNO₂, ....