Coarse-graining (CG) models have greatly extended the spatiotemporal scales of the simulations by integrating away the unnecessary details. This gives an effective speed-up, but the essential physics may be lost or incorrect if the missing degrees of freedom from the CG process involves important information such as conformational or chemical changes. To overcome this limitation, the Ultra-Coarse-Graining (UCG) methodologies have been developed by introducing internal states to CG sites and incorporating state variables into the CG configurational variables. Amongst the various state dynamics, we are specifically interested in the frequent changes of the internal CG states. In this work, we demonstrate the recently developed UCG theory at the quasi-equilibrium limit and apply it to complex soft matter systems. The UCG framework is able to substantially improve the accuracy of the CG model in describing the structural correlations observed in liquid systems. Designed UCG model is capable of capturing the hydrophobic association behavior in liquids, whereas the conventional CG model fails to reproduce this many-body effect. We further extended our approach to construct the UCG model for implicit hydrogen bonding. While the hydrogen bonding geometry is averaged and lost in standard CG models, the UCG model can differentiate between hydrogen bonding donor and acceptor states, capturing the three-body and N-body structural correlations. Furthermore, we tested the applicability of the UCG theory to inhomogeneous interfacial systems. Despite a breakdown of conventional CG models in capturing interface structures, the UCG interface models faithfully reproduce the phase coexistence. Surprisingly, the CG interactions from the UCG interface models quantitatively correspond to the CG bulk liquid interactions, suggesting a new venue of constructing transferable bottom-up CG models. Our findings highlight the advantage of the UCG methodology over conventional CG methods in addressing both accuracy and transferability.

High fidelity ultra-coarse-graining of soft matter systems

2019 Fall National Meeting

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