where u i and v i are the partial molar internal energy and the partial molar volume of component i, respectively. The component-specific factor τ i , which is the cohesive energy of the liquid divided by the activation energy supplied for molecular motion, 27 ranges typically between three and five for liquids. The predictions are included in Figure using τ i = 3.5 (cf. Reference 86 and SI2.6). Since none of the state points chosen for the three considered Lennard-Jones mixtures is in the proximity of the critical point, the model should work well. We performed a detailed uncertainty propagation analysis for the Soret coefficient given by the Shukla-Firoozabadi model (SI2.6). This could explain some of the discrepancies observed between NEMD, EMD, and predictive model results. For mixtures A and C, the model predicts the correct sign and most of the temperature and pressure dependences of S T . The difference between NEMD simulation and model prediction relative to the model uncertainty is, on an average, however as large as 285 % for these two mixtures. While uncertainties cannot be made fully responsible, they could contribute significantly to the deviations. In order to better understand the precise source of the model uncertainty, its relative contributions were calculated (SI2.6, Table ). The by-far largest contribution to the uncertainty in S SF T of component 1 stems from the τ 1 parameter σ τ 1 . The next largest contribution originates usually from σ τ 2 . The critical role of the τ parameters is also reflected in the inability of the model by Shukla and Firoozabadi to predict the correct sign of S T for highly asymmetric mixture B. Here, the regression model by Reith and Müller-Plathe 39 might help shed light onto the reason for the prediction failure.