Dunn Nicholas J H, Noid W G
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Chem Phys. 2015 Dec 28;143(24):243148. doi: 10.1063/1.4937383.
The present work investigates the capability of bottom-up coarse-graining (CG) methods for accurately modeling both structural and thermodynamic properties of all-atom (AA) models for molecular liquids. In particular, we consider 1, 2, and 3-site CG models for heptane, as well as 1 and 3-site CG models for toluene. For each model, we employ the multiscale coarse-graining method to determine interaction potentials that optimally approximate the configuration dependence of the many-body potential of mean force (PMF). We employ a previously developed "pressure-matching" variational principle to determine a volume-dependent contribution to the potential, UV(V), that approximates the volume-dependence of the PMF. We demonstrate that the resulting CG models describe AA density fluctuations with qualitative, but not quantitative, accuracy. Accordingly, we develop a self-consistent approach for further optimizing UV, such that the CG models accurately reproduce the equilibrium density, compressibility, and average pressure of the AA models, although the CG models still significantly underestimate the atomic pressure fluctuations. Additionally, by comparing this array of models that accurately describe the structure and thermodynamic pressure of heptane and toluene at a range of different resolutions, we investigate the impact of bottom-up coarse-graining upon thermodynamic properties. In particular, we demonstrate that UV accounts for the reduced cohesion in the CG models. Finally, we observe that bottom-up coarse-graining introduces subtle correlations between the resolution, the cohesive energy density, and the "simplicity" of the model.
本工作研究了自底向上的粗粒化（CG）方法对分子液体全原子（AA）模型的结构和热力学性质进行精确建模的能力。具体而言，我们考虑了庚烷的1、2和3位点CG模型，以及甲苯的1和3位点CG模型。对于每个模型，我们采用多尺度粗粒化方法来确定相互作用势，该势能最佳地近似多体平均力势（PMF）的构型依赖性。我们采用先前开发的“压力匹配”变分原理来确定势的体积依赖性贡献UV(V)，它近似于PMF的体积依赖性。我们证明，所得的CG模型能够定性但不能定量地准确描述AA密度涨落。因此，我们开发了一种自洽方法来进一步优化UV，使得CG模型能够准确再现AA模型的平衡密度、压缩性和平均压力，尽管CG模型仍然显著低估了原子压力涨落。此外，通过比较这一系列在不同分辨率下准确描述庚烷和甲苯结构及热力学压力的模型，我们研究了自底向上粗粒化对热力学性质的影响。具体而言，我们证明UV解释了CG模型中凝聚力的降低。最后，我们观察到自底向上的粗粒化在分辨率、凝聚能密度和模型的“简单性”之间引入了微妙的相关性。
