Examining normal modes as fundamental heat carriers in amorphous solids: the case of amorphous silicon

TL;DR

This paper critically examines the role of normal modes in heat transport within amorphous silicon, revealing that atomic diffusion and liquid-like dynamics may better explain thermal conductivity than traditional vibrational mode models.

Contribution

It challenges the assumption that individual normal modes are the fundamental heat carriers in amorphous solids, supported by simulations showing significant atomic diffusion.

Findings

Discrepancies in normal mode predictions for amorphous silicon

High-temperature atomic diffusion observed in simulations

Thermal transport may be better described by liquid dynamics

Abstract

Normal mode decomposition of atomic vibrations has been used to provide microscopic under-standing of thermal transport in amorphous solids for decades. In normal mode methods, it is naturally assumed that atoms vibrate around their equilibrium positions and that individual normal modes are the fundamental vibrational excitations transporting heat. With the abundance of predictions from normal mode methods and experimental measurements now available, we care-fully analyze these calculations in amorphous silicon, a model amorphous solid. We find a number of discrepancies, suggesting that treating individual normal modes as fundamental heat carriers may not be accurate in amorphous solids. Further, our classical and ab-initio molecular dynamics simulations of amorphous silicon demonstrate a large degree of atomic diffusion, especially at high temperatures, leading to the conclusion that thermal transport in amorphous solids could be better described starting from the perspective of liquid dynamics rather than from crystalline solids