Nada Hiroki
National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba 305-8569, Japan.
ACS Omega. 2018 May 30;3(5):5789-5798. doi: 10.1021/acsomega.8b00401. eCollection 2018 May 31.
A new methodology for definitively evaluating the structural similarity between different phases in an impartial manner is proposed. This methodology utilizes a dimensionality reduction (DR) technique that was developed in the fields of machine learning and statistics. The basis of the proposed methodology is that the structural similarity between different phases can be evaluated by the geometrical similarity of pair and/or angular distribution functions that reflect the atomic-scale structure of each phase. The DR technique is used for the analysis of this geometrical similarity. In this study, the proposed methodology is applied to evaluate the similarity in the atomic-scale structure, as obtained from molecular dynamics simulations, between amorphous CaCO and CaCO crystal phases in the presence or absence of additives, namely, Mg ions, Sr ions, and water molecules. The results indicate that in the absence of additives, the structure of the amorphous phase is closer to that of vaterite than to those of calcite or aragonite. However, the degree of structural similarity between the amorphous phase and vaterite decreases if Mg ions are present. This tendency is also evident when Sr ions are present, although these ions do not influence the structure of the amorphous phase as strongly as Mg ions. In addition, the results indicate that at a high water concentration, the amorphous phase is separated into small particles by hydrogen-bonded networks of water molecules and the structure of the amorphous phase more closely approaches that of vaterite. The proposed methodology is widely applicable to the evaluation of the structural similarity between different phases for complex multicomponent systems.
提出了一种以公正的方式最终评估不同相之间结构相似性的新方法。该方法利用了机器学习和统计学领域开发的降维（DR）技术。所提出方法的基础是，不同相之间的结构相似性可以通过反映各相原子尺度结构的对和/或角分布函数的几何相似性来评估。DR技术用于分析这种几何相似性。在本研究中，所提出的方法被应用于评估在有无添加剂（即镁离子、锶离子和水分子）的情况下，通过分子动力学模拟获得的非晶态碳酸钙和碳酸钙晶相之间原子尺度结构的相似性。结果表明，在没有添加剂的情况下，非晶相的结构与球霰石的结构比与方解石或文石的结构更接近。然而，如果存在镁离子，非晶相和球霰石之间的结构相似程度会降低。当存在锶离子时，这种趋势也很明显，尽管这些离子对非晶相结构的影响不如镁离子强烈。此外，结果表明，在高水浓度下，非晶相会被水分子的氢键网络分离成小颗粒，并且非晶相的结构更接近球霰石的结构。所提出的方法广泛适用于评估复杂多组分系统中不同相之间的结构相似性。
