Fundamental measure theory for pure systems with soft, spherically repulsive interactions

Fundamental measure theory (FMT) has recently been extended to penetrable spheres and soft spherical interactions (soft-FMT) (Schmidt M 1999 Phys. Rev. E 60 R6291; 2000 J. Phys.: Condens. Matter 11 10 163). This paper presents these theories in a unified description for a pure system and also describes a simple procedure that is thought to improve the accuracy of FMT for soft, spherically repulsive interactions. An ultra-soft interaction, which is a model for the interaction of star polymers with arm number about 8 in a good solvent, is investigated and a simple procedure is found to significantly improve the accuracy of bulk thermodynamic and pair-correlation functions generated by soft-FMT when compared to Monte Carlo simulation results. The simple procedure also improves prediction of the bulk pressure-density relationship for a square-shoulder system. Similar gains in accuracy are expected for a wide range of soft interactions.