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arXiv 1210.4271cond-mat.mtrl-scicond-mat.mes-hall
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MOF-5储氢的van der Waals密度泛函理论研究

Hydrogen storage in MOF-5: A van der Waals density functional theory study

Yue Huang, San-Huang Ke

摘要:

氢分子在金属有机骨架(MOFs)中的物理吸附是一种很有前途的储氢方法,其中范德华力(vdW)起着重要作用,但密度泛函理论(DFT)无法描述。采用vdW密度泛函方法,系统地研究了氢分子在MOF-5晶体中的结合能。我们首先检查这种方法的准确性,通过比较其结果与从晶体中切出的几个片段模型的相关量子化学方法。通过对原始晶胞中吸附一个或多个H $_2$的真实晶体结构的计算,我们发现这些碎片模型不能很好地代表晶体的性质,而这些性质又不能用量子化学方法来处理。发现与有机连接体的结合能远小于与金属氧化物角的结合能,这限制了H $_2$的负载。我们表明,这可以得到显着改善(从5.50至10.39千焦/摩尔),通过用F原子,引起额外的静电相互作用的有机连接体的H原子取代。

英文摘要:

Physisorption of hydrogen molecules in metal-organic frameworks (MOFs) provides a promising way for hydrogen storage, in which the van der Waals (vdW) interaction plays an important role but cannot described by the density functional theory (DFT). By using the vdW density functional (vdW-DF) method, we investigate systematically the binding energies of hydrogen molecules in MOF-5 crystal. We first examine the accuracy of this methodology by comparing its results with those from the correlated quantum chemistry methods for several fragment models cut out from the crystal. Good comparable accuracy is found. By performing calculations for the true crystal structure adsorbing one or multiple H$_2$ in the primitive cell, we show that these fragment models which have been focused previously cannot represent well the property of the crystal which cannot, however, be dealt with by the quantum chemistry methods. It is found that the binding energy with the organic linker is much smaller than with the metal oxide corner, which limits the H$_2$ loading. We show that this can be improved significantly (from 5.50 to 10.39 kJ/mol) by replacing the H atoms of the organic linker with F atoms which cause extra electrostatic interaction.

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