Hybrid WDA: A weighted-density approximation for inhomogeneous fluids

We introduce a density functional approach to inhomogeneous fluids which is an interpolation between the original weighted-density approximation (WDA) and its modified version (MWDA). Our ‘‘hybridized’’ ansatz (HWDA) employs both a locally weighted density like the WDA and an additional globally averaged density like the MWDA. To test the HWDA we calculate triplet direct correlation functions of a homogeneous hard-sphere fluid and the density profiles of a hard-sphere liquid near a hard wall. The HWDA is also applied to the problem of surface segregation in a binary hard-sphere mixture. Comparison with simulation data demonstrates that the HWDA improves the popular MWDA qualitatively as well as quantitatively without spoiling the computational convenience of the latter.