Monitoring local order in the liquid-X interface

Abstract

ABSTRACT We offer a comparison of two different characterizations of favored local structure in an inhomogeneous liquid, using as vehicles simulations of the interfaces between a Lennard-Jones liquid and: (i) a flat Lennard-Jones wall, (ii) the 100 face of a face-centred cubic Lennard-Jones crystal, and (iii) a Lennard-Jones vapor. The interfacial density distributions in (i) and (ii) have oscillations extending several particle diameters into the bulk liquid, while in (iii) it monotonically decays from the bulk liquid to the vapor. We search for transient ordered fluctuations using the Aperture Cross Correlation Function (ACCF) of the system. Particles in the in the two layers closest to the surface of the FCC-liquid interface exhibit a four-fold mirroring of the surface structure; no structure is found elsewhere in this or the other interfaces. The absence of transient ordered structure in the liquid–vapor interface yields a different picture of that interface than derived from the cluster analysis reported by Godonoga et al. (Mol. Phys., 109 (7–10), 1393–1402 (2011)). We argue the advantages of using the ACCF to characterize transient ordered fluctuations as being both experimentally accessible in favourable cases and not reliant on a pre-assumed list of possible structures.