Molecular-dynamics study of a supercooled two-component Lennard-Jones system

Abstract

Molecular-dynamics (MD) simulations have been carried out on a two-component Lennard-Jones system, quenched into supercooled and amorphous states. Two different regimes of viscous behavior are found in the time window accessible in MD simulation studies (of the order of nanoseconds if units appropriate for argon are used). The results for the time dependence of the self-intermediate scattering function ${\mathit{F}}^{\mathit{s}}$(q,t) show two different slow relaxation processes, where the slowest (\ensuremath{\alpha} relaxation) can be represented by a stretched exponential, exp[-(t/${\mathrm{\ensuremath{\tau}}}_{\mathrm{rel}}$${)}^{\mathrm{\ensuremath{\beta}}}$]. In the frequency domain this gives rise to a quasielastic peak, and it is found that its area, the nonergodicity parameter ${\mathit{f}}^{\mathit{s}}$(q)==a, shows an anomalous decrease when increasing the temperature towards a critical value ${\mathit{T}}_{\mathit{c}}$. This happens in the supercooled-liquid regime, and it is one of the basic predictions of the recent mode-coupling theory for the liquid-glass transition problem. In the strongly supercooled-liquid regime the diffusion is of the hopping type, and it is found to be strongly cooperative in nature.