Heterogeneous-homogeneous transition and anomaly of density in SPC/E water examined by molecular dynamics simulations
Heterogeneous-homogeneous transition and anomaly of density in SPC/E water examined by molecular dynamics simulations
复制标题
通过分子动力学模拟检查 SPC/E 水中的异质-均质转变和密度异常
DOI：
10.1016/j.physa.2019.121391
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Habasaki Junko
中科院分区：
文献类型：
--
作者：
Mills P. W.;Rundle R. P.;Samson J. H.;Devitt Simon J.;Tilma Todd;Dwyer V. M.;Everitt Mark J.;Habasaki Junko
利用分子动力学方法对SPC/E水进行了模拟，表征了水的温度依赖性异常，如密度最大值和最小值，以及与之相关的多晶性。本文考虑了解释该系统密度异常的两个重要因素。首先，通过不同类型的局部多面体（O原子围绕O原子通过氢键连接）之间的热力学准平衡来表征水的氢键网络随温度的变化，从而证实了范霍夫分析的适用性。经此处理后，水的结构随温度降低的变化可以表现为由“非均相网络”向“均相网络”的转变。这种解释既不同于简单混合两种（或几种）成分的解释，也不同于仅通过发展典型的氢网络的解释。其次，需要考虑配位壳的振荡结构。对不同长度尺度下的局部密度进行了定量比较，结果表明，较长的长度尺度结构是密度收敛的必要条件。也就是说，水的密度不是不同大小单元的简单和，而是由包含稀疏区域的协调壳决定的。这些概念对于表征水的多变性也很有用。随着200k压力的增大，从“均质网络”向“非均质网络”转变。这种变化对应于从“低密度水”到“高密度水”的变化，并伴随着配位数在更长的尺度上的分布发生较大变化。
Molecular dynamics (MD) simulations of SPC/E water have been performed to characterize anomaly of water such as density maximum and minimum observed in temperature dependence and polyamorphism related them.Two important factors to explain the density anomaly of the system are considered in the present work. First, the changes in network of hydrogen bonds of water with temperatures is characterized by the thermodynamical quasi-equilibration among different kinds of local polyhedra (O atoms around O atom connected by hydrogen bonding), where applicability of the van’t Hoff analysis is confirmed. As a result of this treatment, change of water structure with decreasing temperature can be characterized as the transition from “heterogeneous network” to “homogeneous network”. This explanation differs from that based on simple mixing of two (or several) components nor that by development of typical hydrogen networks only.Second, one needs to consider oscillating structures of coordination shells. Quantitative comparison of local density with different length scales revealed that inclusion of longer length scale structures is required for convergence of the density. Namely, the density of water is not a simple sum of the different size of units but is determined by the coordination shells including sparse regions.These concepts are also useful to characterize the polyamorphism of water. With increasing pressure at 200 K, the transition from “homogeneous network” to “heterogeneous network” occurs. The change corresponds to that from “low density water (LDW)” to “high density water (HDW)”, which accompanied with a large change of distribution of coordination numbers in longer length scales.