Testing mode-coupling theory for a supercooled binary Lennard-Jones mixture. II. Intermediate scattering function and dynamic susceptibility

Abstract

We have performed a molecular dynamics computer simulation of a supercooled binary Lennard-Jones system in order to compare the dynamical behavior of this system with the predictions of the idealized version of mode-coupling theory (MCT). By scaling the time t by the temperature dependent α-relaxation time τ(T), we find that, in the α-relaxation regime, F(q,t) and ${\mathit{F}}_{\mathit{s}}$(q,t), the coherent and incoherent intermediate scattering functions, for different temperatures each follows a q-dependent master curve as a function of scaled time. We show that during the early part of the α relaxation, which is equivalent to the late part of the β relaxation, these master curves are well approximated by the master curve predicted by MCT for the β relaxation. This part is also fitted well by a power law, the so-called von Schweidler law. We show that the effective exponent b′ of this power law depends on the wave vector q if q is varied over a large range. The early part of the β-relaxation regime does not show the critical decay predicted by MCT. The q dependence of the nonergodicity parameter for ${\mathit{F}}_{\mathit{s}}$(q,t) and F(q,t) is in qualitative agreement with MCT. On the time scale of the late α relaxation the correlation functions show a Kohlrausch-Williams-Watts behavior (KWW).