  We study the liquid-vapor phase diagram and the structural properties of
discrete potential fluids by means of Gibbs ensemble simulations and integral
equations theory. We consider three discrete fluids, namely, the square well
(SW), the square well-barrier (SWB), and the square well-barrier-well (SWBW).
They represent simple models for fluids with competing interactions that may
exhibit a rich micro and macroscopic phase behavior depending on both strength
and range of the attractions and repulsions in the potential. Here we emphasize
the structural behavior near the liquid-vapor coexistence. Our findings
indicate that for the SWB fluid a possible scenario of a microscopic phase
separation, associated to a cluster-like formation near the critical region, is
observed and could be understood as a frustration mechanism of the liquid-vapor
transition when either the strength or the range of the repulsion increases.
This microscopic-like separation can be inhibited by suppressing the repulsion
or adding an additional well to the interaction potential. However, in the SW
fluid of long-range potential, we have found results that point out towards
evidence of a microscopic aggregation driven purely by attractions.
