Enhanced septahedral ordering in cold Lennard-Jones fluids

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 < Q(L)(2)>, time-correlation functions, and wavelet density decompositions. The spherical invariants show that noncrystalline septahedral (< Q(7)(2)>) ordering is important, especially at low temperature. While < Q(10)(2)> could arise from icosahedral ordering, its behavior so closely tracks that of the nonicosahedral < Q(11)(2)> that alternative origins for < Q(10)(2)> 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 < Q(7)(2)> increases, especially below T=0.7, but that the correlation length of < Q(5)(2)> is independent of T.