# Boson peak in covalent network glasses: Isostaticity and marginal stability

## TL;DR

This study demonstrates that the boson peak in covalent network glasses like silica is governed by near-isostatic constraints and marginal stability, unifying understanding across different glassy systems through molecular dynamics simulations and experimental data.

## Contribution

It provides the first direct evidence linking the boson peak in covalent glasses to isostaticity and marginal stability, extending concepts from packing-based glasses.

## Key findings

- Boson peak in silica is governed by near-isostatic constraints.
- The boson peak manifests as a wavenumber-independent band in the dynamical structure factor.
- Results are consistent with inelastic X-ray scattering data.

## Abstract

The boson peak (BP) stands as a key feature in understanding glasses and amorphous materials. It directly underlies their anomalous material properties, including thermal behaviors such as excess specific heat and low thermal conductivity, as well as mechanical characteristics such as nonaffine elasticity and fragile plasticity. Despite its importance, understanding of the BP remains limited in covalent network glasses. The most promising concepts are isostaticity and marginal stability, which have been established in theories of rigidity percolation and the jamming transition. While these concepts, supported by comprehensive data, account for the BP in packing-based glasses, comparable explanations have not yet been demonstrated for covalent network glasses. Here we study silica glass, a prototypical covalent network glass, using molecular dynamics simulations. We show that the BP in silica glass is governed by near-isostatic constraints and marginal stability, supporting their universality across diverse glassy systems. Furthermore, we reveal that these principles manifest as a wavenumber-independent band in the dynamical structure factor, and we demonstrate consistency with inelastic X-ray scattering data on silica glass. Our results provide a unified, experimentally testable framework for deciphering the BP and for refining the interpretation of scattering data in amorphous materials.