Density Functionals for Classical Fluids

Classical density functional theory has become a very attractive concept to study both uniform and nonuniform fluids. Its basic theorem states, that the free energy of a given system, viewed as functional of one-particle densities, is uniquely minimized by the equilibrium one-particle density. However, typically the free energy functional for a given system is unknown. As the standard mean field technique to construct density functionals for systems with attractive interactions has obvious deficiencies, an approach, based rather on first-principles to this problem is clearly preferable. To this end, as a contribution of the applicant, the fundamental measure theory and a concept due to Percus were recently merged to analytically construct a free energy functional for sticky spheres. The objective of this research is to extend this combined method to systems with square well (SW) type of interactions. Since already the uniform SW fluid shows interesting phenomena such as the solid-solid transition, the construction of free energy functionals (beyond the mean field format) for SW type of interactions will not only represent the basis for physical (e.g., phase transitions, nucleation, or wetting transitions) and biological (e.g., protein crystallisation) applications, but will also lead to an improved knowledge and modelling of nonuniform systems in technological applications (e.g., chemical engineering or catalysis).