Jin Jaehyeok, Han Yining, Voth Gregory A
Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2019 Apr 21;150(15):154103. doi: 10.1063/1.5067274.
Coarse-grained (CG) models allow efficient molecular simulation by reducing the degrees of freedom in the system. To recapitulate important physical properties, including many-body correlations at the CG resolution, an appropriate mapping from the atomistic to CG level is needed. Symmetry exhibited by molecules, especially when aspherical, can be lost upon coarse-graining due to the use of spherically symmetric CG effective potentials. This mismatch can be efficiently amended by imposing symmetry using virtual CG sites. However, there has been no rigorous bottom-up approach for constructing a many-body potential of mean force that governs the distribution of virtual CG sites. Herein, we demonstrate a statistical mechanical framework that extends a mapping scheme of CG systems involving virtual sites to provide a thermodynamically consistent CG model in the spirit of the principle of maximum entropy. Utilizing the extended framework, this work defines a center of symmetry (COS) mapping and applies it to benzene and toluene systems such that the planar symmetry of the aromatic ring is preserved by constructing two virtual sites along a normal vector. Compared to typical center of mass (COM) CG models, COS CG models correctly recapitulate radial and higher order correlations, e.g., orientational and three-body correlations. Moreover, we find that COS CG interactions from bulk phases are transferable to mixture phases, whereas conventional COM models deviate between the two states. This result suggests a systematic approach to construct more transferable CG models by conserving molecular symmetry, and the new protocol is further expected to capture other many-body correlations by utilizing virtual sites.
粗粒度（CG）模型通过减少系统中的自由度来实现高效的分子模拟。为了概括重要的物理性质，包括CG分辨率下的多体相关性，需要从原子尺度到CG尺度进行适当的映射。分子所表现出的对称性，尤其是非球形分子的对称性，在粗粒度过程中可能会因使用球对称的CG有效势而丧失。通过使用虚拟CG位点施加对称性，可以有效地修正这种不匹配。然而，目前还没有一种严格的自下而上的方法来构建控制虚拟CG位点分布的多体平均力势。在此，我们展示了一个统计力学框架，该框架扩展了涉及虚拟位点的CG系统的映射方案，以根据最大熵原理提供一个热力学一致的CG模型。利用这个扩展框架，这项工作定义了一个对称中心（COS）映射，并将其应用于苯和甲苯系统，通过沿着法向量构建两个虚拟位点来保持芳香环的平面对称性。与典型的质心（COM）CG模型相比，COS CG模型能够正确地概括径向和高阶相关性，例如取向和三体相关性。此外，我们发现来自体相的COS CG相互作用可以转移到混合相，而传统的COM模型在这两种状态之间存在偏差。这一结果表明了一种通过保留分子对称性来构建更具转移性的CG模型的系统方法，并且预计新协议将通过利用虚拟位点捕获其他多体相关性。
