The structure of simple liquids

Perturbation theories have proved to be reliable methods for the description of structure and thermodynamics of liquids. In this work two of them will be examined more closely: the Weeks-Chandler-Andersen-approximation, which takes the softness of a given potential into account add the Optimized Random-Phase approximation, which describes the attractive part of the interaction. After a test of the numerical procedure for a model-liquid, the Square-Well system, which shows very good agreement with data taken from computer experiments, the above mentioned perturbation theories are applied to a real system, to liquid Rubidium. As it was surmised during the last years, the influence of the long range part of the potential (Friedel-oscillations) is shown to be most important for the structure of the liquid. Besides that the well known corrections for the softness of the repulsive part of the potential are reproduced. Beyond that, agreement between the theoretical results and the neutron-diffraction-data is excellent for low and intermediate temperatures (1400-1600 K). Anyway this procedure fails to describe the structure factor for small momentum transfers for those systems, where the mean-free path of the electrons is about of the same magnitude as the interatomic distance, which is for temperatures around 1600 K and more. (Author)