Non-equilibrium molecular dynamics (NEMD) simulations closely mimic experimental scenarios to study thermodiffusion because these simulations exhibit regions of high and low temperature within the simulation volume. Furthermore, linear concentration profiles and linear temperature profiles in between these regions are obtained at steady state, the latter implying a constant thermal conductivity. The thermal conductivity of pure Lennard-Jones fluids and binary mixtures increases with temperature and density, the two effects possibly compensating each other. Thus, a narrow region in the center of the simulation volume is defined as a heat source and a corresponding region as a heat sink at the edges of the simulation volume in z direction (Figure ). The temperature profile T (z) and the mole fraction profiles x i (z) were determined on the basis of particle trajectories obtained with LAMMPS 58 (stable version: October 29, 2020). Both temperature-control regions were of equal size, having a width of 0.3σ 1 if not stated otherwise, where σ 1 is the Lennard-Jones size parameter of component 1. The resulting width was typically ≈1 % of the simulation volume. Two Langevin thermostats were used, where one thermostat heated one temperature-control region and the other thermostat cooled the other T -control region, so that we refer to this method as Langevin NEMD.