应用分子动力学模拟和拉曼光谱对钙、镁、氯离子 水化现象的研究

应用分子动力学方法，模拟了298 K下，密度为1.0 g/cm~3的水溶液中Ca²⁺,Mg²⁺,Cl~-的水化现象，得到了相应离子周围水分子的微观分布情况.发现在钙离子周围，水分子以其氧离子去靠近中心离子；而在氯离子周围，水分子则以其中的一个氢原子去靠近中心离子.通过分析三种离子的径向分布函数、配位数曲线、水化数、水化半径，发现Ca²⁺的水化数和水化半径均大于Mg²⁺,即Ca²⁺的水合能力比Mg²⁺强.与以往研究结果相比，本文计算所得的自扩散系数更接近实验所得结果.为了使模型更好的代表真实水溶液体系，本文还应用分子动力学和拉曼光谱法研究了不同浓度的CaCl₂水溶液.分子动力学研究发现随着浓度的升高，CaCl₂溶液中Ca²⁺,Cl~-的配位数分别呈降低趋势.同时，随着浓度的升高，Ca²⁺,Cl~-的自扩散系数也呈现降低的趋势.作者推断这是由于浓度的升高，加剧了离子的微观反...

Application of molecular dynamics simulation and Raman spectroscopy to study the hydration phenomena of calcium, magnesium and chloride ions

Using molecular dynamics method, the hydration phenomenon of Ca2+, Mg2+, Cl- in an aqueous solution with a density of 1.0g/cm3 at 298 K was simulated, and the microscopic distribution of water molecules around the corresponding ions was obtained. It was found that around calcium ions, water molecules approached the central ion by oxygen ions; around chloride ions, water molecules approached the central ion by the hydrogen atoms. By analyzing the radial distribution function, coordination number curve, hydration number, and hydration radius, it was found that the hydration number and hydration radius of Ca2+ were greater than those of Mg2+. Therefore, it was speculated that the hydration capacity of Ca2+ was stronger than that of Mg2+. In order to simulate the real aqueous system, the microstructure of CaCl2 aqueous solutions at different concentrations were studied by molecular dynamics and Raman spectroscopy. Molecular dynamics studies found that with the increase of concentration, the coordination number of Ca2+ and Cl- in CaCl2 solution showed a decreasing trend. At the same time, as the concentration increases, the self-diffusion coefficients of Ca2+ and Cl- also showed a decreasing trend. This may be caused by the microscopic reverse motion of the ions. The Raman results showed that with the increase of CaCl2 concentration, the hydrogen bond network structure in the solution was damaged severely. And there appeared more contact ion pairs formed by Ca2+ and Cl-.