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刚体水模型中的热力学、扩散和结构异常。

Thermodynamic, diffusional, and structural anomalies in rigid-body water models.

机构信息

Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi, India.

出版信息

J Phys Chem B. 2011 Jun 2;115(21):6935-45. doi: 10.1021/jp110695t. Epub 2011 May 10.

Abstract

Structural, density, entropy, and diffusivity anomalies of the TIP4P/2005 model of water are mapped out over a wide range of densities and temperatures. The locus of temperatures of maximum density (TMD) for this model is very close to the experimental TMD locus for temperatures between 250 and 275 K. Four different water models (mTIP3P, TIP4P, TIP5P, and SPC/E) are compared with the TIP4P/2005 model in terms of their anomalous behavior. For all the water models, the density regimes for anomalous behavior are bounded by a low-density limit at around 0.85-0.90 g cm(-3) and a high-density limit at about 1.10-1.15 g cm(-3). The onset temperatures of the density anomaly in the various models show a much greater variation, ranging from 202 K for mTIP3P to 289 K for TIP5P. The order maps for the various water models are qualitatively very similar with the structurally anomalous regions almost superimposable in the q(tet)-τ plane. Comparison of the phase diagrams of water models with the region of liquid-state anomalies shows that the crystalline phases are much more sensitive to the choice of water models than the liquid state anomalies; for example, SPC/E and TIP4P/2005 show qualitatively similar liquid state anomalies but very different phase diagrams. The anomalies in the liquid in all the models occur at much lower pressures than those at which the melting line changes from negative to positive slope. The results in this study demonstrate several aspects of structure-entropy-diffusivity relationships of water models that can be compared with experiment and used to develop better atomistic and coarse-grained models for water.

摘要

全面考察了 TIP4P/2005 模型水在较宽密度和温度范围内的结构、密度、熵和扩散率异常。该模型的最大密度温度(TMD)轨迹非常接近实验 TMD 轨迹,实验温度范围在 250 到 275 K 之间。将四种不同的水模型(mTIP3P、TIP4P、TIP5P 和 SPC/E)与 TIP4P/2005 模型进行了比较,比较了它们的异常行为。对于所有的水模型,异常行为的密度范围都受到低密度限制,大约在 0.85-0.90 g cm(-3),高密度限制在大约 1.10-1.15 g cm(-3)。各种模型中密度异常的起始温度变化很大,从 mTIP3P 的 202 K 到 TIP5P 的 289 K。各种水模型的有序映射在 q(tet)-τ 平面上具有非常相似的结构异常区域,定性上非常相似。将水模型的相图与液态异常区域进行比较表明,与液态异常相比,晶相对水模型的选择更为敏感;例如,SPC/E 和 TIP4P/2005 表现出相似的液态异常,但相图却非常不同。所有模型中的液态异常发生的压力远低于熔融线从负斜率变为正斜率的压力。本研究的结果展示了水模型的结构-熵-扩散率关系的几个方面,可以与实验进行比较,并用于开发更好的原子和粗粒水模型。

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