Using this method to study small systems, where the length of the simulation parallel to the heat flux, l z , is comparable to the phonon mean free path (MFP), can result in the emergence of finite size effects. The MFP represents the average distance a phonon travels before colliding with other energy carriers. In small systems, incomplete phonon scattering events and boundary reflections lead to under predictions in thermal conductivity estimates, compared to 'bulk' systems. To check for possible finite size effects in our systems, the simulation box was replicated in the z axis, parallel to the heat flux, and the thermal conductivity was recalculated. No significant difference in thermal conductivity, indicating that the results were size independent and therefore a 70 × 70 × 70 Å3 simulation box was sufficiently large enough to directly obtain the bulk thermal conductivity.