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arXiv 0808.3154cond-mat.mtrl-sci
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小水团簇中氢键的DFT交换相关泛函的精确性II:水的六聚体和范德华相互作用

On the accuracy of DFT exchange-correlation functionals for H bonds in small water clusters II: The water hexamer and van der Waals interactions

Biswajit Santra, Angelos Michaelides, Martin Fuchs, Alexandre Tkatchenko, Claudia Filippi, Matthias Scheffler

摘要:

采用完全基组(CBS)极限下的二阶Moeller-Plesset微扰理论(MP2)和扩散量子Monte Carlo(DMC)方法对水六聚体的几种低能异构体进行了研究。这两种方法都预测所谓的“棱镜”是能量最低的异构体,其次是“笼”,“书”和“环状”异构体。四种异构体的能量非常相似,都在10-15 meV/H2O之间。该参考数据然后被用来评估几个密度泛函理论(DFT)交换相关(xc)泛函的性能。针对较小的水簇测试的xc泛函的子集[I:Santra等人,127,184104(2007)]中所描述的。虽然某些泛函在预测各种异构体的绝对离解能(在10-20 meV/H2O范围内)方面做了合理的工作,但没有预测四种异构体的正确能量顺序,也没有预测正确的低总能量异构体。所有的xc泛函测试预测书或环状异构体具有最大的离解能。一个多体分解内的六聚体的总相互作用能导致的结论是,失败在于在考虑的xc泛函的范德华力(分散)的描述不佳。它示出的经验成对(有吸引力的)C6/R6校正某些泛函的添加允许改进的能量排序的六聚体。这些结果的相关性密度泛函模拟液态水也进行了简要讨论。

英文摘要:

Second order Moeller-Plesset perturbation theory (MP2) at the complete basis set (CBS) limit and diffusion quantum Monte Carlo (DMC) are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called "prism" to be the lowest energy isomer, followed by "cage", "book", and "cyclic" isomers. The energies of the four isomers are very similar, all being within 10-15 meV/H2O. This reference data is then used to evaluate the performance of several density-functional theory (DFT) exchange-correlation (xc) functionals. A subset of the xc functionals tested for smaller water clusters [I: Santra et al., J. Chem. Phys. 127, 184104 (2007)] has been considered. Whilst certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers (coming within 10-20 meV/H2O), none predict the correct energetic ordering of the four isomers, nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals (dispersion) forces in the xc functionals considered. It is shown that the addition of an empirical pairwise (attractive) C6/R6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.

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