水合锰(Ⅱ)结构的量子化学和ABEEM/MM研究

Studies of the hydration structures of manganous(Ⅱ) via the quantum chemistry and ABEEM/MM Models

应用新一代可极化分子力场——原子-键电负性均衡浮动电荷分子力场ABEEM/MM,结合精密量子化学方法,构建了精确的Mn2+-H2O相互作用的势能函数,确定了相关参数.将该势能函数用于计算[Mn(H2O)n]2+(n=1～12)的结构和结合能,得到了与量子化学一致的结果.进一步对Mn2+水溶液进行ABEEM/MM动力学模拟,得到的Mn2+–O径向分布函数的第一和第二最高峰分别处于0.218和0.435nm处,积分得到第一和第二水合层的配位水分子数分别为7.03和17.74;对于O–Mn2+–O角度分布函数,其第一和第二最高峰分别位于80°和140°附近,这些结果与实验和其他理论方法的结果有很好的一致性.Mn2+的极化作用使得第一水合层中水分子的键长明显增长,键角明显减小;而Mn2+对第二水合层及外层水分子的结构影响较小.分析体系的电荷分布表明,与ABEEM-7P纯水相比,Mn2+水溶液中参与形成氢键的氢原子和孤对电子的电荷变化较大,且Mn2+和其邻近的水分子间存在明显的电荷转移.

For the next-generation polarizable force field, atom-bond electronegativity equalization fluctuating charge force field （ABEEM/MM）, and quantum chemistry method, an accurate Mn2＋-H2O potential function was constructed, and its parameters were determined via fitting to quantum chemistry results. Then the potential function was employed to calculate the structure and binding energies of the hydrated manganous ionic clusters Mn2＋（H2O）n （n=1–12）. The results were in good agreement with those from quantum chemistry. Furthermore, the structural properties of the Mn2＋ aqueous solution were simulated using ABEEM/MM molecular dynamics. This includes the radial distribution function （RDF）, angular distribution function （ADF）, water structure, and charge distribution. The first and second peaks of Mn2＋-O RDF are located at 0.218 nm and 0.435 nm. The coordination numbers for the first and second hydration shells, which were integrated from the RDF, are 7.03 and 17.74. The first and second peaks of the O–Mn2＋–O ADF are located at 80° and 140°. These results are consistent with those from experimental measurements and other theoretical simulations. The water molecules in the first hydration shell were polarized by the Mn2＋ ions, and their bond lengths were stretched, but their bond angles were reduced. Mn2＋ does not measurably affect the structures of the water molecules outside the first hydration shell. Our analysis of the charge distributions showed that, compared with ABEEM-7P liquid water, the charges of the H atom and lone pairs vary more in the Mn2＋ aqueous solution. Moreover, there was evident charge transfer between the Mn2＋ ions and their adjacent water molecules.