Molecular dynamics simulations in hybrid particle-continuum schemes: Pitfalls and caveats

Abstract

Heterogeneous multiscale methods (HMM) combine molecular accuracy of particle-based simulations with the computational efficiency of continuum descriptions to model flow in soft matter liquids. In these schemes, molecular simulations typically pose a computational bottleneck, which we investigate in detail in this study. We find that it is preferable to simulate many small systems as opposed to a few large systems, and that a choice of a simple isokinetic thermostat is typically sufficient while thermostats such as Lowe-Andersen allow for simulations at elevated viscosity. We discuss suitable choices for time steps and finite-size effects which arise in the limit of very small simulation boxes. We also argue that if colloidal systems are considered as opposed to atomistic systems, the gap between microscopic and macroscopic simulations regarding time and length scales is significantly smaller. We propose a novel reducedorder technique for the coupling to the macroscopic solver, which allows us to approximate a non-linear stress-strain relation efficiently and thus further reduce computational effort of microscopic simulations. best attributes of both parts: the molecular accuracy with the computational efficiency of continuum models.

Colloidal Shear-Thickening Fluids Using Variable Functional Star-Shaped Particles: A Molecular Dynamics Study

“…In the model we studied, the fluid is Newtonian for small packing fractions, but develops a yield stress as the packing fraction increases, similar to several previous works [65,[69][70][71][72], as seen in Figure 2a-c. One can see the rise of solid-like properties in those fluidic systems.…”

Shear-Thinning in Oligomer Melts—Molecular Origins and Applications

“…Discretisation in space is realised by the discontinuous Galerkin (dG) method [ 68 , 69 , 70 ]. Domain is discretised by a quadrilateral mesh with a meshsize h .…”

Shear-thinning in Polymer Melts -- Molecular Origins and Hybrid Multiscale Simulations

“…These small differences might be attributed to the neglect of forces arising from the thermostat in the stress calculation or an effect observed in Ref. [48], where it was shown that the specific coupling of shear to thermostats may introduce small discrepancies in the calculation of viscosity. In Figure 1b we investigate the dependence of viscosity on shear rate as a function of stiffness for a polymer melt with chain length N = 15.…”