Fast Simulation of Binary Mixtures: Quantifying Diffusion with Changes in Roughness

What is it about?

Molecular Dynamics (MD) simulations enable the analysis of processes and systems that are challenging, dangerous, or simply time-consuming in experiments, or are even not yet synthesized. To save time and computing resources, so-called coarse-grained models are used. They also enable the simulation of systems that are otherwise too large or too long to be simulated with each atom represented individually. Several atoms are grouped together into one bead. This reduces the number of particles that have to be simulated and thereby significantly decreases the computational costs needed. While many structural and thermodynamic properties can be matched accurately, dynamical properties are usually accelerated compared to realistic values from experiments or atomistic simulations. The here applied RoughMob method (Roughness and Mobility) quantifies the change in surface roughness to predict the acceleration of mobility upon coarse-graining. The work demonstrates how the method can be applied to binary mixtures of hydrocarbon liquids.

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Photo by Alexander Grey on Unsplash

Photo by Alexander Grey on Unsplash

Why is it important?

1. Efficient simulation of binary hydrocarbon mixtures Fluid mixtures are, e.g., widely used in industrial processes, where the knowledge of diffusion coefficients can be a prerequisite for the design of efficient process plants. Already a binary mixture requires a large amount of simulation to test different possible compositions, which increases drastically if there are more different compositions to choose from. Here, the RoughMob method reduces both time and computational demands, enhancing the efficiency of simulation studies. 2. Step towards more complex systems The dynamical properties of more complex or larger systems such as polymer melts are not accessible via molecular dynamics simulations in full atomistic detail at all. Thus, a proper means that allows calculating the dynamical properties of these systems from simple coarse-grained simulations is highly desirable and would greatly expand the application range of MD simulations. The size of hydrocarbon molecules that are coarse-grained into one bead per molecule reflects the size and level of coarse-graining typically used for polymer chains. The calculation on fluid mixtures presented here is a necessary step toward the application of RoughMob to polymers.