# Short-range dynamics in the solid and liquid phases

## TL;DR

This paper investigates the short-range dynamics and the phonon-roton minimum in solids and liquids through experiments, simulations, and theory, revealing their common origin in interatomic interactions.

## Contribution

It provides a comprehensive study combining INS experiments, MD simulations, and theoretical analysis to explain the phonon-roton minimum across phases.

## Key findings

- Identification of short-range order dependence in different phases
- Comparison of excitation spectra between crystals and liquids
- Theoretical explanation of phonon-roton minima as a classical phenomenon

## Abstract

The existence of the phonon-roton minimum has been widely observed for both the solid and liquid phases but so far there is no sufficient theoretical explanation of its origin. In this paper we use a range of techniques to study the dynamics and short-range order for a range of simple materials in their crystalline, amorphous and liquid phases. We perform inelastic neutron scattering (INS) experiments of polycrystalline and liquid barium to study the high-frequency dynamics and understand the mechanisms underlying the atomic motion. Moreover we perform INS simulations for crystals and supercooled liquids, compare the collective excitation spectra and identify similarities. We perform molecular dynamics (MD) simulations for the same materials and present results of population and bond angle distribution showing a short-range order dependence of the different phases, expanding the current knowledge in literature. Finally, we support our findings with a theoretical explanation of the origin of the phonon-roton minima which is observed in both solids and liquids. We study this as a classical phenomenon and we base our explanation on short range interatomic interactions.