  A two-component system of penetrable particles interacting via a gaussian
core potential is considered, which may serve as a crude model for binary
polymer solutions. The pair structure and thermodynamic properties are
calculated within the random phase approximation (RPA) and the hypernetted
chain (HNC) integral equation. The analytical RPA predictions are in
semi-quantitative agreement with the numerical solutions of the HNC
approximation, which itself is very accurate for gaussian core systems. A
fluid-fluid phase separation is predicted to occur for a broad range of
potential parameters. The pair structure exhibits a nontrivial clustering
behaviour of the minority component. Similiar conclusions hold for the related
model of parabolic core mixtures, which is frequently used in dissipative
particle dynamics (DPD) simulations.
