Energy Renormalization for Coarse-Graining the Dynamics of a Model Glass-Forming Liquid

Abstract

Coarse-grained modeling achieves the enhanced computational efficiency required to model glass-forming materials by integrating out "unessential" molecular degrees of freedom, but no effective temperature transferable coarse-graining method currently exists to capture dynamics. We address this fundamental problem through an energy-renormalization scheme, in conjunction with the localization model of relaxation relating the Debye-Waller factor ⟨u⟩ to the structural relaxation time τ. Taking ortho-terphenyl as a model small-molecule glass-forming liquid, we show that preserving ⟨u⟩ (at picosecond time scale) under coarse-graining by renormalizing the cohesive interaction strength allows for quantitative prediction of both short- and long-time dynamics covering the entire temperature range of glass formation. Our findings provide physical insights into the dynamics of cooled liquids and make progress for building temperature-transferable coarse-grained models that predict key properties of glass-forming materials.

Energy Renormalization Method for the Coarse-Graining of Polymer Viscoelasticity

“…We recently proposed an energy-renormalization (ER) approach to capturing AA polymer dynamics under coarse-graining 25,26 by renormalizing the cohesive interaction strength parameter ε (via the “entropy−enthalpy compensation” effect) 34–38 in a temperature-dependent manner, i.e., ε(T)=α(T)ε0 where α( T ) is a renormalization factor and ε 0 is a constant value. The sigmoidal variation of α( T ) [and ε ( T )] obtained from our ER method is consistent with the variation of the extent of collective motion (or alternatively, the size evolution of the cooperatively rearranging regions) predicted by the GET of glass formation.…”

“…In our prior works, we demonstrated that by borrowing ideas from the generalized entropy theory (GET) and the Adam−Gibbs theory of glass formation, we could correct the accelerated dynamics of the CG model in a temperature-transferable manner. 25,26 This was done by realizing that E a can be “renormalized” by tuning the cohesive interaction strength parameter ε , which is readily accessible in commonly used nonbonded potentials such as the Lennard-Jones (LJ) potentials. The influence of ε on polymer dynamics has been vindicated in recent simulations.…”

Energy Renormalization for Coarse‐Graining Polymers with Different Fragilities: Predictions from the Generalized Entropy Theory

“…We next turn to the issue of CG modeling of polymer melts within the framework of GET. The recent ER method provides an attractive approach for quantitatively describing the dynamics of the underlying AA polymer models under coarse‐graining over a wide temperature range 21,22,27. In the previous formulation of ER method, the CG models of polymers are developed by the exploiting the localization model of relaxation that relates the Debye–Waller factor (DWF; i.e., a fast‐dynamics property at a picosecond timescale) to τ α in MD simulations.…”

“…Notably, the ER method has been recently tested for three distinct CG models of polymers having different segmental structures, that is, polybutadiene (PB), polystyrene (PS), and polycarbonate (PC), which can capture the AA dynamics to a good approximation 22. This method also works reasonably well for a model of a small‐molecule GF liquid, ortho‐terphenyl (OTP) 21. More details regarding the CG modeling via the ER method and its formulation can be found in our recent studies 22,27,48.…”

“…To address this fundamental problem, we recently proposed a coarse‐graining strategy, called the energy‐renormalization (ER) approach, which aims to preserve essential dynamic properties of GF liquids to a good approximation 20–22. By borrowing ideas from the Adam–Gibbs (AG) theory16 and the more recent generalized entropy theory (GET) of glass formation,23 both of which emphasize the central role of configurational entropy in describing the dynamics of GF liquids, we introduce the ER factors to rescale the energy parameter ε in the cohesive interaction (based on the established “entropy–enthalpy compensation” effect)24–26 in a temperature dependent manner to recover the dynamics of polymers over a wide temperature range, that is, from the high‐temperature Arrhenius to low‐temperature supercooled and even glassy regimes 22,27.…”