\section{Further work}

In light of the fact that the Kempers model is likely fundamentally flawed, the search for an approach to developing a first-principles model of the Soret effect should continue. Approaches with their roots in irreversible thermodynamics or transition theory are so far largely unable to reproduce gas-phase behaviour.\cite{soret_review_2022} For large, complex molecules, kinetic gas theory is also known to be imprecise.\cite{kinetic_review} In light of this, it should be recognised that modern developments within computer simulations the past 10-20 years greatly facilitates the expansion of an accurate kinetic theory to more advanced molecules, and the possibility of using a kinetic theory in combination with one of the aforementioned approaches to modelling thermal diffusion may be fruitful to pursue.

Work has been conducted on incorporating long time-correlations into a kinetic theory to account for cage- and vortex effects that become significant at high densities.\cite{kinetic_review} Furthermore, there have been attempts at including vibrational and rotational terms to the energy transfer into the Chapman-Enskog solution method.\cite{vibrational_enskog,vibrational_enskog_2,vib_enskog_3} These are interesting developments, that appear fruitful to follow further. The implementation of the Enskog solutions developed in this work may prove useful in this regard. If one wishes to accurately describe more advanced systems, having a good starting point that is reliable for simple molecules at low-medium densities is a necessary prerequisite. 

The solution implemented here for Mie potentials is valid for an arbitrary spherical potential, which makes it possible to use in combination with somewhat more complex potentials, such as the Feynman-Hibbs quantum corrected Mie potential.\cite{saft_mixtures} This potential has been shown to reliably reproduce the low-temperature behaviour of some fluids that are poorly described by the Mie potential. The approach used in this work; using a potential that gives reliable predictions for equilibrium properties in combination with the Enskog solutions, should be investigated further, as it appears to be fruitful. Regarding the fact that parameters fit to equilibrium data yield reliable predictions regarding transport phenomena: It is tempting to suggest that one could fit parameters to measured transport coefficients before using them to model equilibrium behaviour. There are likely several potential pitfalls to this approach, but a preliminary investigation into its feasibility may be of interest.