title: A Gaussian theory for fluctuations in simple liquids.
abstract: Assuming an effective quadratic Hamiltonian, we derive an approximate, linear stochastic equation of motion for the density-fluctuations in liquids, composed of overdamped Brownian particles. From this approach, time dependent two point correlation functions (such as the intermediate scattering function) are derived. We show that this correlation function is exact at short times, for any interaction and, in particular, for arbitrary external potentials so that it applies to confined systems. Furthermore, we discuss the relation of this approach to previous ones, such as dynamical density functional theory as well as the formally exact treatment. This approach, inspired by the well known Landau-Ginzburg Hamiltonians, and the corresponding "Model B" equation of motion, may be seen as its microscopic version, containing information about the details on the particle level.
authors.affiliation: 4th Institute for Theoretical Physics, Universität Stuttgart, 70569 Stuttgart, Germany and Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Krüger
authors.affiliation: Laboratoire Ondes et Matière d'Aquitaine (LOMA), University Bordeaux and CNRS, UMR 5798, F-33400 Talence, France.
authors.forename: David S
authors.initials: DS
authors.lastname: Dean