Entropy of flexible liquids from hierarchical force-torque covariance and coordination
Entropy of flexible liquids from hierarchical force-torque covariance and coordination
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DOI：
10.1080/00268976.2018.1459002
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发表时间：
2018-01-01
影响因子：
1.7
通讯作者：
Henchman, Richard H.
中科院分区：
文献类型：
--
作者：
Higham, Jonathan;Chou, Szu-Yu;Henchman, Richard H.
提出了用分子动力学模拟计算柔性分子液体的熵的新理论。熵由两个项表示：振动项，表示能量势垒中构型和动量态的平均数；地形项，表示能量势垒的有效数目。振动项以分层的方式从两个力-力矩协方差矩阵中得到，一个在分子水平上，一个在联合原子水平上。地形项包括构象和取向，它们分别由二面体分布和配位数得出。该方法在14种液体上进行了测试，范围从氩气到环己烷。对于大多数分子，我们的结果在实验范围内，略高于2pt方法的结果，2pt方法是目前唯一能够直接计算此类体系的熵的方法。该理论不仅提供了一种计算熵的有效而实用的方法，而且对分子结构进行了全面的表征和量化。
New theory is presented to calculate the entropy of a liquid of flexible molecules from a molecular dynamics simulation. Entropy is expressed in two terms: a vibrational term, representing the average number of configurations and momentum states in an energy well, and a topographical term, representing the effective number of energy wells. The vibrational term is derived in a hierarchical manner from two force-torque covariance matrices, one at the molecular level and one at the united-atom level. The topographical term comprises conformations and orientations, which are derived from the dihedral distributions and coordination numbers, respectively. The method is tested on 14 liquids, ranging from argon to cyclohexane. For most molecules, our results lie within the experimental range, and are slightly higher than those by the 2PT method, the only other method currently capable of directly calculating entropy for such systems. As well as providing an efficient and practical way to calculate entropy, the theory serves to give a comprehensive characterisation and quantification of molecular structure.[GRAPHICS].