One-dimensional phonon effects in direct molecular dynamics method for thermal conductivity determination

We demonstrate that the use of the direct, heat source/sink method for thermal conductivity determination via molecular dynamics simulation leads to diverging thermal conductivity with increasing simulation cell length when the cross section of the cell is kept constant. A phonon transport theory based analysis shows that this divergence arises due to discrete phonon phase space sampling leading to behavior characteristics of one-dimensional systems, which are known for size divergent thermal conductivity. We also show that the divergence is particularly strong for thermal conductivity along the elastically soft direction in anisotropic crystals.