Department of Chemistry, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok, Thailand.
J Phys Chem B. 2011 Nov 3;115(43):12527-36. doi: 10.1021/jp204809f. Epub 2011 Oct 10.
The ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism was applied to simulate carbonate and nitrate anions in aqueous solution. The out-of-plane (ν(2)) spectra obtained from the velocity autocorrelation functions (VACFs) and the torsion angle-time functions indicate that the symmetry of carbonate is reduced from D(3h) to a lower degree by breaking up the molecular plane, whereas the planarity of nitrate anion is retained. The calculated frequencies are in good agreement with the Raman and IR data. Carbonate shows a stronger molecular hydration shell than the nitrate anion with the average molecular coordination numbers of 8.9 and 7.9, respectively. A comparison with the average number of ion-solvent hydrogen bonds (H-bonds) indicates the extra water molecules within the hydration shell of carbonate (∼2) and nitrate (∼3), readily migrating from one coordinating site to another. The mean residence times for water ligands in general classify carbonate and nitrate as moderate and weak structure-making anions, while the specific values for individual sites of nitrate reveal local weak structure-breaking properties.
我们应用从头算量子力学电荷场分子动力学（QMCF MD）理论模拟了水溶液中的碳酸根和硝酸根阴离子。从速度自相关函数（VACFs）和扭转角-时间函数得到的面外（ν(2)）谱表明，碳酸根的分子平面被打破后，其对称性从 D(3h)降低到较低程度，而硝酸根阴离子保持平面性。计算得到的频率与拉曼和红外数据吻合较好。碳酸根比硝酸根具有更强的分子水化壳，平均分子配位数分别为 8.9 和 7.9。与离子-溶剂氢键（H-bonds）的平均数量相比，碳酸根（约 2）和硝酸根（约 3）的水化壳内有额外的水分子，它们容易从一个配位位点迁移到另一个配位位点。水配体的平均停留时间通常将碳酸根和硝酸根归类为中等和弱的结构形成阴离子，而硝酸根各个位点的具体值则显示出局部的弱结构破坏性质。
