Medium-range order in a simple monatomic liquid

The origin of intermediate-range structure in a simple monatomic liquid is analysed using the concept of vacancy ordering. The liquid, simulated by molecular dynamics, features an anomalous long-wavelength prepeak in its structure factor, a signature of structural order at intermediate distances. We present convincing evidence that this structural anomaly can be accounted for by the ordering of vacancy-like voids in the structure. It is concluded that the presence of well-defined atom-sized voids, as well as their participation in the medium-range structure may be explained by the predominantly icosahedral local order of this liquid. The results of this study are thus relevant to simple metallic glass-formers which possess a similar type of local order. (C) 1998 Published by Elsevier Science B.V. All rights reserved.