Modeling of neutron and x-ray scattering by liquids: The risks of using phenomenological models

We review exact formalisms for describing the dynamics of liquids in terms of static parameters. We discuss how these formalisms are prone to suffer from imposing restrictions that appear to adhere to common sense, but which are overly restrictive, resulting in a flawed description of the dynamics. We detail a fail-safe way for modeling the scattering data of liquids that are free from any unwarranted restriction and avoid overparametrizations. We also list some common habits in analyzing the data and discuss how often they do not do justice to the accuracy achieved in scattering experiments, thus frequently leading to overinterpretations in place of a better-grounded model rejection.