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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Cluster model for the ionic product of water: Accuracy and limitations of common density functional methods
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Cluster model for the ionic product of water: Accuracy and limitations of common density functional methods

机译：水离子产物的簇模型：普通密度泛函方法的准确性和局限性

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摘要

In the present study, the performance of six popular density functionals (B3LYP, PBE0, BLYP, BP86, PBE, and SVWN) for the description of the autoionization process in the water octamer was studied. As a benchmark, MP2 energies with complete basis sets limit extrapolation and CCSD(T) correction were used. At this level, the autoionized structure lies 28.5 kcal(.)mol(-1) above the neutral water octamer. Accounting for zero-point energy lowers this value by 3.0 kcal(.)mol(-1). The transition state of the proton transfer reaction, lying only 0.7 kcal(.)mol(-1) above the energy of the ionized system, was identified at the MP2/aug-cc-pVDZ level of theory. Different density functionals describe the reactant and product with varying accuracy, while they all fail to characterize the transition state. We find improved results with hybrid functionals compared to the gradient-corrected ones. In particular, B3LYP describes the reaction energetics within 2.5 kcal(.)mol(-1) of the benchmark value. Therefore, this functional is suggested to be preferably used both for Carr-Parinello molecular dynamics and for quantum mechanics/ molecular mechanics (QM/MM) simulations of autoionization of water.
机译：在本研究中，研究了六种流行的密度泛函（B3LYP，PBE0，BLYP，BP86，PBE和SVWN）的性能，用于描述水八聚体中的自电离过程。作为基准，使用了具有完整基集极限外推法和CCSD（T）校正的MP2能量。在这个水平上，自电离结构位于中性水八聚体上方28.5 kcal（。）mol（-1）。考虑到零点能量会使此值降低3.0 kcal（。）mol（-1）。在理论上的MP2 / aug-cc-pVDZ水平上，质子转移反应的过渡态仅比电离体系的能量高0.7 kcal（.mol）（-1）。不同密度的官能团以不同的精度描述反应物和产物，而它们都无法表征过渡态。与梯度校正的函数相比，我们发现混合函数的结果更好。特别地，B3LYP描述了在基准值的2.5 kcal（.mol）（-1）内的反应能。因此，建议将该功能优选同时用于Carr-Parinello分子动力学和水离子化的量子力学/分子力学（QM / MM）模拟。

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