【摘要】 通过理论计算推测 NH- 2 ,NH3 和 NH+4在水溶液第一溶剂化层中与之直接作用的水分子分别为 2 ,4和 4个 ,并采用离散 -连续模型计算了 NH- 2 ,N H3 和 NH+ 4在水溶液中的溶剂化自由能 .结果表明 ,由于离散 -连续模型在从头算水平考虑了溶质分子与第一溶剂化层溶剂分子之间的作用 ,能更准确地描述溶剂化作用 .此外 ,采用更加符合溶液中真实情况的溶剂化构型 ,能得到更准确的溶剂化性质 .更多还原

【Abstract】 The solvation free energies of NH- 2, NH 3, and NH + 4 in aqueous solution were calculated by means of a mixed discrete-continuum model, in which the solute and a limited number of solvent molecules were treated quantum chemically and the remaining solvent was simulated by the polarizable continuum model(PCM) method. The numbers of water molecules hydrogen-bonding directly with NH- 2, NH 3, and NH+ 4 are predicted to be 2, 4, and 4 respectively at the HF level. By comparing with the results obtained with the PCM method, our results show that because specific solute-solvent interactions are described at the quantum level and long-range interactions are introduced through a continuum model, the discrete-continuum model could simulate the solvation effects more accurately than the continuum model, especially in case where the solvent and the solute are strongly bound. The predicted solvation free energies for NH- 2 and NH+ 4 are in good agreement with available experimental data. Due to the explicit consideration of specific solute-solvent interactions, the electron correlation effect is significant in the discrete-continuum model. Furthermore, from the gas phase to the solution, the large changes of geometries of hydrated solutes caused by the continuum field suggest that the geometry reoptimization in the solvent is necessary. In the discrete-continuum model, the geometries of hydrated ions closer to the real case would lead more accurate solvation free energies.更多还原