Computer Simulations of Thermal Diffusion in Binary Fluid Mixtures

Abstract

Compared to other transport properties, thermal diffusion has not been much studied by computer simulations. During the last decade, however, a couple of different simulation methods have been applied to a few systems, aiming both at determination of numerical values of the Soret coefficient and at a better understanding of the phenomenon. Based on such simulations, we will present some explanations for why there is a Soret effect in binary fluids.

The computer simulation methods may be put in two main categories; equilibrium molecular dynamics (MD) simulations using Green-Kubo formalism to derive the transport coefficients, and non-equilibrium methods (NEMD) using linear response theory to derive the coefficients. The NEMD methods are in turn of two types, synthetic NEMD where the external thermodynamic force is built into the equations of motion for the system, and boundary-driven NEMD, where the external force stems from perturbations of the systems boundaries. We will discuss possibilities and limitations with these methods, and what we have learned from the simulations.

Some possibilities for future simulation work will be outlined, e.g. coupled transport processes across interfaces and in porous media.