Calculating lattice thermal conductivity: A comparative study on carbon nanotubes.

Carbon nanotubes (CNTs) are commonly utilized in nanoscale devices. High structural order, rigid sp²-bonds and a low atomic mass result in an exceptionally high lattice thermal conductivity (TC), which motivates their use in applications demanding efficient heat removal. However, pinpointing exact TC values of individual defect-free CNTs remains a challenge both experimentally and computationally. The thermal transport properties of ideal CNTs are dominated by phonon-phonon scattering, and a theoretical prediction of TC has to include anharmonic terms in the interatomic potential energy which give rise to phonon-phonon interaction. Here we compare two computational frameworks that take into account lattice anharmonicity to predict TC: classical molecular dynamics (MD) vs. anharmonic lattice calculation (ALC). Taking the same empirical interaction potential as input to both MD and ACL, we contrast phonon-phonon scattering rates and TC results as a function of temperature. This comparison also allows us to critically evaluate several assumptions in the different methods, namely the description of anharmonicity by a truncated Taylor expansion of the interaction potential in ALC, the use of classical phonon statistics in MD, and the importance of Umklapp processes for the TC.