  Phase behavior of the Yukawa hard-sphere polydisperse mixture with high
degree of polydispersity is studied using high temperature approximation (HTA)
and mean spherical approximation (MSA). We have extended and applied the scheme
developed to calculate the phase diagrams of polydisperse mixtures described by
the truncatable free energy models, i.e., the models with Helmholtz free energy
defined by the finite number of the moments of the species distribution
function. At high degree of polydispersity, several new features in the
topology of the two-phase diagram have been observed: the cloud and shadow
curves intersect twice and each of them forms a closed loop of the
ellipsoidal-like shape with the liquid and gas branches of the cloud curve
almost coinciding. Approaching a certain limiting value of the polydispersity
index, the cloud and shadow curves shrink and disappear. Beyond this limiting
value, polydispersity induces the appearance of the three-phase equilibrium at
lower temperatures. We present and analyze corresponding phase diagrams
together with distribution functions of three coexisting phases. In general,
good agreement was observed between predictions of the two different
theoretical methods, i.e., HTA and MSA. Our results confirm qualitative
predictions for the three-phase coexistence obtained earlier within the
framework of the van der Waals approach.
