XH-NH3(X=F,Cl,Br)质子传递的溶剂效应:簇模型,连续介质模型和离散-连续组合模型的比较

分别采用分子簇模型、连续介质模型和离散-连续组合模型研究了XH-NH3(X=F，Cl，Br)分子内质子传递的溶剂效应．结果表明，对于弱酸性化合物FH-NH3，其溶剂效应主要为短程作用，3个H2O分子即可使其发生质子传递，而简单的连续介质模型得到的仍为分子化合物形式，需进一步包含溶剂效应短程作用．对于强酸性化合物ClH-NH3和BrH-NH3，较弱的溶剂效应即可促使其发生质子传递，分子簇模型和连续介质模型均可合理描述，且与离散-连续组合模型的结果相近．离散-连续组合模型既在从头算水平考虑了溶质分子和第一溶剂化层中溶剂分子间的短程作用，又包含了溶剂效应的长程静电作用，能更准确地描述溶剂化作用，且对弱酸性化合物和强酸性化合物体系均适用．

Solvent Effect on Proton Transfer in Ammonia-hydrogen Halide Complexes:Comparison of Cluster,Continuum and Combined Discrete-continuum Models

Solvent effects on proton transfer in ammonia-hydrogen halide complexes have been investigated by using the cluster, continuum, and combined discrete-continuum models, respectively. Our results show that for the hydrogen-bonded complexes with less acidic HF subunit, the structure obtained by the continuum model is of neutral type whereas in clusters with at least three molecules of water the ion pair structures have been found. These results suggest that for such hydrogen bonded complex the simple continuum model is not adequate and explicit water molecules should be added in order to take into account specific hydrogen bonds. For the hydrogen-bonded complexes with strong acidic HCl and HBr subunits, a weak solvent effect is adequate to describe proton transfer processes in aqueous solution. The ion pair structures have been found by using the cluster model or the continuum model, and their results are in agreement with those in the combined discrete-continuum model. Because specific solute-solvent interactions were described at the quantum level and long-range interactions were introduced through a continuum model, the combined discrete-continuum model would lead to more accurate solvation properties and was suitable for hydrogen-bonded complexes with both strongly and weakly acidic HX subunit.