Zielkiewicz Jan
Department of Chemistry, Gdańsk University of Technology, Poland.
J Chem Phys. 2005 Sep 8;123(10):104501. doi: 10.1063/1.2018637.
Molecular-dynamics simulations were carried out for the SPC, SPCE, TIP4P, and TIP5P models of water at 298 K. From these results we determine the following quantities: the absolute entropy using the two-particle approximation, the mean lifetime of the hydrogen bond, the mean number of hydrogen bonds per molecule, and the mean energy of the hydrogen bond. From the entropy calculations we find that nearly all contributions to the total entropy originates from the orientation effects. Moreover, we determine the contributions to the total entropy which originate from the first, second, and higher solvation shells. It is interesting that the limits between solvation shells are clearly visible. The first solvation shell (0.22 < r < 0.36 nm) contributes approximately 43 J mol K to the total entropy; the second solvation shell (0.36 < r < 0.60 nm) contributes approximately 12 J mol K, while contributions from the third and other solvation shells are very small, approximately 2 J mol K in summary. This indicates that water molecules are strongly ordered up to 0.55-0.6 nm around the central water molecule, and beyond this limit the ordering diminishes. The results of calculations (entropy and hydrogen bonds) are compared with the experimental data for the choosing of the best water model. We find that the SPC and TIP4P models reproduce the best experimental values, and we recommend these models for computer simulations of the aqueous solution of biomolecules.
在298K下对水的SPC、SPCE、TIP4P和TIP5P模型进行了分子动力学模拟。根据这些结果，我们确定了以下量：使用双粒子近似法计算的绝对熵、氢键的平均寿命、每个分子的平均氢键数以及氢键的平均能量。从熵的计算中我们发现，对总熵的几乎所有贡献都源于取向效应。此外，我们确定了来自第一、第二和更高溶剂化层对总熵的贡献。有趣的是，溶剂化层之间的界限清晰可见。第一溶剂化层（0.22 < r < 0.36 nm）对总熵的贡献约为43 J·mol⁻¹·K⁻¹；第二溶剂化层（0.36 < r < 0.60 nm）的贡献约为12 J·mol⁻¹·K⁻¹，而第三和其他溶剂化层的贡献非常小，总计约为2 J·mol⁻¹·K⁻¹。这表明水分子在中心水分子周围0.55 - 0.6 nm范围内强烈有序排列，超过这个限度，有序性就会减弱。将计算结果（熵和氢键）与实验数据进行比较，以选择最佳的水模型。我们发现SPC和TIP4P模型能最好地重现实验值，我们推荐这些模型用于生物分子水溶液的计算机模拟。
