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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >An Improved Cluster Pair Correlation Method for Obtaining the Absolute Proton Hydration Energy and Enthalpy Evaluated with an Expanded Data Set
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An Improved Cluster Pair Correlation Method for Obtaining the Absolute Proton Hydration Energy and Enthalpy Evaluated with an Expanded Data Set

机译：改进的簇对相关方法，用于获得质子水合绝对能量和扩展数据集的焓

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An improved cluster pair correlation method that is based on the method originally introduced by Tuttle et al. (Tuttle et al. J. Phys. Chem. A 2002. 106. 925-932) was developed and evaluated using a significantly larger data set than used previously. With this larger data set. values for the absolute proton hydration free energy of -259.3 and -265.0 kcal/mol were obtained using the original and improved method, respectively. The former value is ~4.5 kcal/mol less negative than previously reported values obtained with the same method but with smaller data sets. The dependence of this value on data set size indicates that the uncertainty in the original method may be greater than previously realized. The improved method has the advantages of higher precision, and the effects of cluster size on the proton hydration free energy and enthalpy values can be more readily evaluated. Data for ions with extreme pK_as. many of which were included in previous estimates of the proton hydration free energy, were found to be unreliable and were eliminated from the extended data set. There is only a subtle effect of cluster size on the Gibbs free energy values, and within the limits of the approximation inherent in the cluster pair correlation method, the "best" value for the standard absolute proton hydration free energy obtained with this new method and larger data set is -263.4 kcal/mol (average for clusters with 4-6 water molecules). The absolute proton hydration enthalpy values decrease from -273.1 to -275.3 kcal/mol with increasing cluster size (one to six water molecules, respectively). This trend, along with an anomalously high value for the absolute proton hydration entropy, indicates that the enthalpy obtained with this method may not have converged for these relatively small clusters.
机译：一种改进的簇对关联方法，该方法基于Tuttle等人最初引入的方法。 （Tuttle等人，J.Phys.Chem.A 2002.106.925-932）已经开发并使用比以前使用的大得多的数据集进行了评估。有了这个更大的数据集。分别使用原始方法和改进方法获得的绝对质子水合自由能的值分别为-259.3和-265.0 kcal / mol。前一个值比使用相同方法但数据集更小的先前报告的值少约4.5 kcal / mol的负值。该值对数据集大小的依赖性表明，原始方法中的不确定性可能大于先前实现的不确定性。改进后的方法具有精度较高的优点，并且可以更容易地评估簇大小对质子水合自由能和焓值的影响。极端pK_as的离子数据。先前对质子水合自由能的估计中包括了许多，但发现这些方法不可靠，因此已从扩展数据集中将其消除。团簇大小对吉布斯自由能值只有微妙的影响，并且在簇对关联方法固有的近似范围内，通过这种新方法获得的标准绝对质子水合自由能的“最佳”值和较大的数据集为-263.4 kcal / mol（具有4-6个水分子的簇的平均值）。随着团簇尺寸的增加，质子水合绝对焓值从-273.1降低到-275.3 kcal / mol（分别为一到六个水分子）。这种趋势，加上绝对质子水化熵的异常高值，表明用这种方法获得的焓可能尚未收敛于这些相对较小的簇。

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