Density dependence of thermal conductivity in nanoporous and amorphous carbon with machine-learned molecular dynamics

TL;DR

This study uses machine-learned molecular dynamics to analyze how density affects thermal conductivity in nanoporous and amorphous carbon, revealing different dependence patterns linked to structural motifs and order.

Contribution

It introduces a large-scale MD simulation approach with a machine-learned potential to systematically study structure-dependent thermal transport in disordered carbon.

Findings

Thermal conductivity shows linear density dependence in nanoporous carbon.

Amorphous carbon exhibits superlinear density dependence of thermal conductivity.

Structural motifs and order significantly influence heat transport properties.

Abstract

Disordered forms of carbon are an important class of materials for applications such as thermal management. However, a comprehensive theoretical understanding of the structural dependence of thermal transport and the underlying microscopic mechanisms is lacking. Here we study the structure-dependent thermal conductivity of disordered carbon by employing molecular dynamics (MD) simulations driven by a machine-learned interatomic potential based on the efficient neuroevolution potential approach. Using large-scale MD simulations, we generate realistic nanoporous carbon (NP-C) samples with density varying from $0.3$ to $1.5$ g cm$^{-3}$ dominated by sp$^2$ motifs, and amorphous carbon (a-C) samples with density varying from $1.5$ to $3.5$ g cm$^{-3}$ exhibiting mixed sp$^2$ and sp$^3$ motifs. Structural properties including short- and medium-range order are characterized by atomic coordination, pair correlation function, angular distribution function and structure factor. Using the homogeneous nonequilibrium MD method and the associated quantum-statistical correction scheme, we predict a linear and a superlinear density dependence of thermal conductivity for NP-C and a-C, respectively, in good agreement with relevant experiments. The distinct density dependences are attributed to the different impacts of the sp$^2$ and sp$^3$ motifs on the spectral heat capacity, vibrational mean free paths and group velocity. We additionally highlight the significant role of structural order in regulating the thermal conductivity of disordered carbon.