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This paper series aims to establish a complete correspondence between fine-grained (FG) and coarse-grained (CG) dynamics by way of excess entropy scaling (introduced in Paper I). While Paper II successfully captured translational motions in CG systems using a hard sphere mapping, the absence of rotational motions in single-site CG models introduces differences between FG and CG dynamics. In this third paper, our objective is to faithfully recover atomistic diffusion coefficients from CG dynamics by incorporating rotational dynamics. By extracting FG rotational diffusion, we unravel, for the first time reported to our knowledge, a universality in excess entropy scaling between the rotational and translational diffusion. Once the missing rotational dynamics are integrated into the CG translational dynamics, an effective translation-rotation coupling becomes essential. We propose two different approaches for estimating this coupling parameter: the rough hard sphere theory with acentric factor (temperature-independent) or the rough Lennard-Jones model with CG attractions (temperature-dependent). Altogether, we demonstrate that FG diffusion coefficients can be recovered from CG diffusion coefficients by (1) incorporating “entropy-free” rotational diffusion with translation-rotation coupling and (2) recapturing the missing entropy. Our findings shed light on the fundamental relationship between FG and CG dynamics in molecular fluids.
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Representability and Dynamical Consistency in Coarse-Grained Models
We address the challenge of representativity and dynamical consistency when un- bonded fine-grained particles are collected together into coarse-grained particles. We implement a hybrid procedure for identifying and tracking the underlying fine-grained particles—e.g., atoms or molecules—by exchanging them between the coarse-grained particles periodically at a characteristic time. The exchange involves a back-mapping of the coarse-grained particles into fine-grained particles, and a subsequent reassign- ment to coarse-grained particles conserving total mass and momentum. We find that an appropriate choice of the characteristic exchange time can lead to the correct effec- tive diffusion rate of the fine-grained particles when simulated in hybrid coarse-grained dynamics. In the compressed (supercritical) fluid regime, without the exchange term, fine-grained particles remain associated to a given coarse-grained particle, leading to substantially lower diffusion rates than seen in all-atom molecular dynamics of the fine- grained particles. Thus, this work confirms the need for addressing the representativity of fine-grained particles within coarse-grained particles, and offers a simple exchange mechanism so as to retain dynamical consistency between the fine- and coarse- grained scales.
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- Award ID(s):
- 2102455
- PAR ID:
- 10537480
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry B
- Volume:
- 128
- Issue:
- 6
- ISSN:
- 1520-6106
- Page Range / eLocation ID:
- 1506 to 1514
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpcb.3c08054
