Glass forming phase diagram and local structure of Kob-Andersen binary Lennard-Jones nanoparticles

Zhongquan Chen; Weikai Qi; Richard K Bowles

doi:10.1063/1.5047465

Glass forming phase diagram and local structure of Kob-Andersen binary Lennard-Jones nanoparticles

J Chem Phys. 2018 Sep 7;149(9):094502. doi: 10.1063/1.5047465.

Authors

Zhongquan Chen¹, Weikai Qi¹, Richard K Bowles¹

Affiliation

¹ Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.

PMID: 30195318
DOI: 10.1063/1.5047465

Abstract

Molecular dynamics simulation is used to study glass formation in Kob-Andersen binary Lennard-Jones nanoparticles and determine the glass forming phase diagram for the system as a function of composition. The radial distribution function, a Steinhardt bond-orientational order parameter, and favored local structure analysis are used to distinguish between glassy and ordered systems. We find that surface enrichment of the large atoms alters the nanoparticle core composition, leading to an overall shift of the glass forming region to lower small atom mole fractions, relative to the bulk system. At small atom mole fraction, x_B = 0.1, the nanoparticles form a solid with an amorphous core, enriched with the small atoms, surrounded by a partially ordered surface region, enriched with the large atom component. The most disordered glass nanoparticles occur at x_B ≈ 0.3, but the surface-core enrichment leads to the crystallization of the nanoparticle to the CsCl crystal above x_B ≈ 0.35, which is lower than observed in the bulk. The glass transition temperatures of the nanoparticles are also significantly reduced. This allows the liquid to remain dynamic to low temperatures and sample the low energy inherent structure minima on the potential energy surface containing a high abundance of favoured local structures.