We have considered a classical lattice-gas model, consisting of a two-dimensional lattice Z2, each site of which hosts at most one two-component unit vector; particles occupying pairs of nearest-neighbouring sites interact via the ferromagnetic potential [Formula: see text] where νj=0,1 denotes occupation numbers, uj are the unit vectors (classical spins) and ∊ is a positive constant setting energy and temperature scales; the total Hamiltonian is given by [Formula: see text] where ∑{j<k} denotes sum over all distinct nearest-neighbouring pairs of lattice sites. The saturated-lattice version of this model, where all sites are occupied, supports the well-known Berezhinskiĭ–Kosterlitz–Thouless transition; we report here a simulation study, carried out for both μ= 0.1 and μ=-0.2, showing evidence of a transition of this kind, in broad qualitative agreement with previous Renormalization-Group studies.
Equilibrium states for a classical lattice gas