  We reconsider model II of [J. Chem. Phys. 1968, 49, 1778--1783], a
two-dimensional lattice-gas system featuring a crystalline phase and two
distinct fluid phases (liquid and vapor). In this system, a particle prevents
other particles from occupying sites up to third neighbors on the square
lattice, while attracting (with decreasing strength) particles sitting at
fourth- or fifth-neighbor sites. To make the model more realistic, we assume a
finite repulsion at third-neighbor distance, with the result that a second
crystalline phase appears at higher pressures. However, the similarity with
real-world substances is only partial: on closer inspection the alleged
liquid-vapor transition turns out to be a continuous (albeit sharp) crossover,
even near the putative triple point. Closer to the standard picture is instead
the freezing transition, as we show by computing the free-energy barrier to
crystal nucleation from the "liquid".
