Enhanced septahedral ordering in cold Lennard-Jones fluids

Abstract

We report molecular dynamics calculations on a two-component, cold, 15,625 particle, three-dimensional Lennard-Jones fluid. We calculated spherical harmonic components Q(LM) for the density of particles in the first coordination shell of each particle, as well as their spherical invariants <Q2L>, time-correlation functions, and wavelet density decompositions. The spherical invariants show that noncrystalline septahedral (<Q27>) ordering is important, especially at low temperature. While < Q210> could arise from icosahedral ordering, its behavior so closely tracks that of the nonicosahedral <Q211> that alternative origins for <Q210> need to be considered. Time correlation functions of spherical harmonic components are bimodal, with a faster temperature-independent mode and a slow, strongly temperature-dependent mode. Volume wavelet decompositions show that when T is reduced, the correlation length of <Q27> increases, especially below T=0.7 , but that the correlation length of <Q25> is independent of T .