Influence of the coordination defects on the dynamics and the potential energy landscape of two-dimensional silica

TL;DR

This study investigates how coordination defects influence the energy landscape and dynamics of 2D silica, revealing a low-energy cutoff that explains the fragile-to-strong crossover and showing similarities with 3D silica behavior.

Contribution

It identifies the microscopic origin of the fragile-to-strong crossover in 2D silica through defect analysis and energy landscape parameters, extending understanding from 3D silica.

Findings

Low-energy cutoff exists in defect and defect-free states.

Fragile-to-strong crossover relates to energy landscape parameters.

Similar low-temperature behavior observed in 2D and 3D silica.

Abstract

The main cause of the fragile-to-strong crossover of 3D silica was previously attributed to the presence of a low energy cutoff in the potential energy landscape. The important question emerges about the microscopic origin of this crossover and the generalizibility to other glass-formers. In this work, the fragile-to-strong crossover of a model 2D glassy system is analyzed via molecular dynamics simulation, which represents 2D-silica. By separating the sampled defect and defect-free inherent structures, we are able to identify their respective density of state distributions with respect to energy. A low energy cutoff is found in both distributions. It is shown that the fragile-to-strong crossover can be quantitatively related to the parameters of the energy landscape, involving in particular the low-energy cutoff of the energy distribution. It is also shown that the low-energy cutoff of the defect-states is determined by the formation energy of a specific defect configuration, involving two silicon and no oxygen defect. The low-temperature behavior of 2D silica is quantitatively compared with that of 3D silica, showing surprisingly similar behavior.