Szukalo Ryan J, Noid W G
Department of Chemistry, Penn State University, University Park, PA 16802 United States of America.
J Phys Condens Matter. 2021 Feb 24;33(15). doi: 10.1088/1361-648X/abdff8.
By eliminating unnecessary details, coarse-grained (CG) models provide the necessary efficiency for simulating scales that are inaccessible to higher resolution models. However, because they average over atomic details, the effective potentials governing CG degrees of freedom necessarily incorporate significant entropic contributions, which limit their transferability and complicate the treatment of thermodynamic properties. This work employs a dual-potential approach to consider the energetic and entropic contributions to effective interaction potentials for CG models. Specifically, we consider one- and three-site CG models for ortho-terphenyl (OTP) both above and below its glass transition. We employ the multiscale coarse-graining (MS-CG) variational principle to determine interaction potentials that accurately reproduce the structural properties of an all-atom (AA) model for OTP at each state point. We employ an energy-matching variational principle to determine an energy operator that accurately reproduces the intra- and inter-molecular energy of the AA model. While the MS-CG pair potentials are almost purely repulsive, the corresponding pair energy functions feature a pronounced minima that corresponds to contacting benzene rings. These energetic functions then determine an estimate for the entropic component of the MS-CG interaction potentials. These entropic functions accurately predict the MS-CG pair potentials across a wide range of liquid state points at constant density. Moreover, the entropic functions also predict pair potentials that quite accurately model the AA pair structure below the glass transition. Thus, the dual-potential approach appears a promising approach for modeling AA energetics, as well as for predicting the temperature-dependence of CG effective potentials.
通过消除不必要的细节，粗粒度（CG）模型为模拟更高分辨率模型无法触及的尺度提供了必要的效率。然而，由于它们对原子细节进行了平均，支配CG自由度的有效势必然包含显著的熵贡献，这限制了它们的可转移性，并使热力学性质的处理变得复杂。这项工作采用双势方法来考虑对CG模型有效相互作用势的能量和熵贡献。具体而言，我们考虑了在玻璃化转变温度之上和之下的邻三联苯（OTP）的单点和三点CG模型。我们采用多尺度粗粒化（MS-CG）变分原理来确定相互作用势，该势能够在每个状态点精确再现OTP全原子（AA）模型的结构性质。我们采用能量匹配变分原理来确定一个能量算符，该算符能够精确再现AA模型的分子内和分子间能量。虽然MS-CG对势几乎是纯排斥的，但相应的对能量函数具有一个明显的最小值，该最小值对应于相互接触的苯环。这些能量函数进而确定了MS-CG相互作用势的熵分量的估计值。这些熵函数在恒定密度下的广泛液态点范围内准确预测了MS-CG对势。此外，熵函数还预测了对势，该对势能够相当准确地模拟玻璃化转变温度以下的AA对结构。因此，双势方法似乎是一种用于模拟AA能量学以及预测CG有效势的温度依赖性的有前途的方法。
