A local order metric for condensed phase environments

TL;DR

This paper presents a local order metric (LOM) that quantifies the degree of local structural order in condensed matter environments, effectively distinguishing between crystals, liquids, and amorphous states.

Contribution

The paper introduces the LOM, a novel quantitative measure of local order that improves resolution in characterizing structural environments in condensed phases.

Findings

LOM values range from 0 (disordered) to 1 (perfectly ordered).

LOM and derived parameters accurately differentiate structural phases.

Application to simulations reveals insights into nucleation and amorphization processes.

Abstract

We introduce a local order metric (LOM) that measures the degree of order in the neighborhood of an atomic or molecular site in a condensed medium. The LOM maximizes the overlap between the spatial distribution of sites belonging to that neighborhood and the corresponding distribution in a suitable reference system. The LOM takes a value tending to zero for completely disordered environments and tending to one for environments that match perfectly the reference. The site averaged LOM and its standard deviation define two scalar order parameters, $S$ and $\delta S$, that characterize with excellent resolution crystals, liquids, and amorphous materials. We show with molecular dynamics simulations that $S$, $\delta S$ and the LOM provide very insightful information in the study of structural transformations, such as those occurring when ice spontaneously nucleates from supercooled water or when a supercooled water sample becomes amorphous upon progressive cooling.