The Reith-Müller-Plathe model consists of three additive quadratic functions, each of which was separately fitted to a series of NEMD-derived Soret coefficients. In each series, a single model parameter of component 1, m 1 , σ 1 , or ε 1 , was systematically varied so that the impact of one model parameter was encoded in one quadratic function. The resulting overall Soret coefficient, which was successfully validated on realistic systems such as isotopic argon-argon, argon-krypton and xenon-methane, is given by 39