A spin-1 Ising model incorporating positional order to a standard lattice gas
with no attractive interactions is introduced and found to be consistent with
all known attributes of the freezing transition of the hard-sphere system.
Implementation of attractive interactions in a fairly natural way then allows
every aspect of the phase diagram of a simple substance to be reproduced. The
\emph{whole} phase behavior of such sort of substances is thus found to sharply
manifest the van der Waals picture highlighting the relevance of harsh
repulsive forces.Comment: 10 pages, 4 figure