A numerical study of longtime dynamics and ergodic-nonergodic transitions in dense simple fluids

Abstract

For over 30 years, mode-coupling theory (MCT) has been the de facto theoretic description of dense fluids and the liquid-glass transition. MCT, however, is limited by its ad hoc construction and lacks a mechanism to institute corrections. We use recent results from a new theoretical framework--developed from first principles via a self-consistent perturbation expansion in terms of an effective two-body potential--to numerically explore the kinetics of systems of classical particles, specifically hard spheres obeying Smoluchowski dynamics. We present here a full solution to the kinetic equation governing the density-density time correlation function and show that the function exhibits the characteristic two-step decay of supercooled fluids and an ergodic-nonergodic transition to a dynamically-arrested state. Unlike many previous numerical studies and experiments, we have access to the full time and wavenumber range of the correlation function and can track the solution unprecedentedly close to the transition, covering nearly 15 decades of time. Using asymptotic approximation techniques developed for MCT, we fit the solution to predicted forms and extract critical parameters. Our solution shows a transition at packing fraction $η^*=0.60149761(10)$--consistent with previous static solutions under this theory and with comparable colloidal suspension experiments--and the behavior in the $β$-relaxation regime is fit to power-law decays with critical exponents $a=0.375(3)$ and $b=0.8887(4)$, and with $λ=0.5587(18)$. For the $α$-relaxation of the ergodic phase, we find a power-law divergence of the time scale $τ_α$ as we approach the transition. Through these results, we establish that this new theory is able to reproduce the salient features of MCT, but has the advantages of a first principles derivation and a clear mechanism for making systematic improvements.