The Langevin NEMD simulations were typically carried out with 1200 molecules. The z direction of the simulation volume was divided into 50 bins of constant width ∆z = l z /50 (Figure ). Each molecule i was assigned to one of the bins j, according to its position z i : j = int(z i /∆z). For each bin j, the kinetic energy of all molecules located in the bin E kin (z j ) was determined where N(z j ) is the number of molecules in bin j, m i and v i the mass and the velocity of molecule i, respectively, and v is the center-of-mass velocity of the system. Since the total momentum of the system was set to zero, v vanishes. The local temperature in bin j T (z j ) was calculated by 35