Ab-initio heat transport in defect-laden quasi-1D systems from a symmetry-adapted perspective

TL;DR

This work addresses how structural symmetry governs phonon-mediated heat transport in defect-laden quasi-1D nanotubes. It introduces a symmetry-resolved mode-resolved Green's function framework based on line-group theory to classify phonons by irreps and enforce acoustic and rotational sum rules, enabling precise, artefact-free transmission calculations. By applying this to multi-layer WS$_2$-MoS$_2$ nanotubes with controlled defects, the authors show that symmetry breaking can open new transmission channels and, in some cases, enhance thermal conductance, a result confirmed by finite-temperature MD that includes anharmonic effects. The approach offers a transferable, efficient means to design nanoscale heat-management components by exploiting symmetry to tailor phonon transport.

Abstract

Due to their aspect ratio and wide range of thermal conductivities, nanotubes hold significant promise as heat-management nanocomponents. Their practical use is, however, often limited by thermal resistance introduced by structural defects or material interfaces. An intriguing question is the role that structural symmetry plays in thermal transport through those defect-laden sections. To address this, we develop a framework that combines representation theory with the mode-resolved Green's function method, enabling a detailed, symmetry-resolved analysis of phonon transmission through defected segments of quasi-1D systems. To avoid artifacts inherent to formalisms developed for bulk 3D systems, we base our analysis on line groups, the appropriate description of the symmetries of quasi-1D structures. This categorization introduces additional quantum numbers that partition the phonon branches into smaller, symmetry-distinct subsets, enabling clearer mode classification. We employ an Allegro-based machine learning potential to obtain the force constants and phonons with near-ab-initio accuracy. We calculate detailed phonon transmission profiles for single- and multi-layer MoS$_\mathrm{2}$-WS$_\mathrm{2}$ nanotubes and connect the transmission probability of each mode to structural symmetry. Surprisingly, we find that pronounced symmetry breaking can suppress scattering by relaxing selection rules and opening additional transmission channels. Molecular dynamics shows that the behavior persists even when anharmonicity is considered. The fact that higher disorder introduced through defects can enhance thermal transport, and not just suppress it, demonstrates the critical role of symmetry in deciphering the nuances of nanoscale thermal transport.

Figures (11)

• Figure 1: Structures, numbers of atoms, and numbers of configurations included in the ab-initio dataset.
• Figure 2: Schematic diagram of AGF's structural partitioning (Left lead, scattering region, and right lead), which determines the shape of the IFC matrices.
• Figure 3: Flowchart illustrating the additional steps in the mode-resolved AGF method.
• Figure 4: Parity plots for the total energy and the forces over the training and validation sets: MLIP vs DFT ground truth.
• Figure 5: Phonon vibration modes associated to four different values of $m$ at the $\Gamma$ point $(*){q=0}$ of a pristine single-walled WS2 nanotube.