It is well known that small molecular systems under periodic boundary conditions are associated with systematic errors when diffusion coefficients are calculated. In this context, the size dependence of the mass-mass L 11 and internal energy-mass L E1 phenomenological coefficients was studied for one of the considered systems (i.e., mixture B2). A series of simulations with varying system size containing 600, 1200, 2400, 4800 and 8000 molecules was performed. As expected, a clear system size dependence was observed for the mass-mass phenomenological coefficient L 11 (Figure ). Its value in the thermodynamic limit, obtained by extrapolation to infinite size, was found to be 5.5% higher than its sampled value for 1200 molecules. Therefore, L 11 had to be corrected to account for finite size effects when working with small systems, for example, as proposed in Reference 81. A finite size correction of L 11 based on a modified version of the correction factor by Yeh and Hummer 82;83 for binary mixtures yields an improvement, but L 11 remains underestimated by 4%. On the other hand, no clear system size dependence could be inferred for the internal energy-mass coefficient L E1 despite its diffusive nature (Figure ).