Density functional for additive mixtures

We present a density functional theory for mixtures of particles interacting with a radially symmetric pair potential. The approach is suitable for systems with soft or hard interactions between like species. The cross interactions between unlike species are restricted to obey an additivity constraint. The functional is a generalization of the soft fundamental measure theory (SFMT) for one-component systems and reduces to Rosenfeld's functional in the case of hard sphere mixtures. It respects both, the zero-dimensional limit and the virial expansion. The structure of the homogeneous fluid phase is an output. As an application, we calculate the pair distributions of colloidal hard spheres mixed with star polymers and find good agreement with computer simulation results.