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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Accurate Treatment of Electrostatics during Molecular Adsorption in Nanoporous Crystals without Assigning Point Charges to Framework Atoms
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Accurate Treatment of Electrostatics during Molecular Adsorption in Nanoporous Crystals without Assigning Point Charges to Framework Atoms

机译：在纳米孔晶体分子吸附过程中对静电的精确处理，而无需将电荷分配给骨架原子

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摘要

Molecular simulations have become an important complement to experiments for studying gas adsorption and separation in crystalline nanoporous materials. Conventionally, these simulations use force fields that model adsorbate—pore interactions by assigning point charges to the atoms of the adsorbent. The assignment of framework charges always introduces ambiguity because there are many different choices for defining point charges, even when the true electron density of a material is known. We show how to completely avoid such ambiguity by using the electrostatic potential energy surface (EPES) calculated from plane wave density functional theory (DFT). We illustrate this approach by simulating CO2 adsorption in four metal—organic frameworks (MOFs): IRMOF-1, ZIF-8, ZIF-90, and Zn(nicotinate)2. The resulting CO2 adsorption isotherms are insensitive to the exchange-correlation functional used in the DFT calculation of the EPES but are sensitive to changes in the crystal structure and lattice parameters. Isotherms computed from the DFT EPES are compared to those computed from several point charge models. This comparison makes possible, for the first time, an unbiased assessment of the accuracy of these point charge models for describing adsorption in MOFs. We find an unusually high Henry's constant (109 mmol/g · bar) and intermediate isosteric heat of adsorption (34.9 kj/mol) for Zn(nicotinate)2, which makes it a potentially attractive material for CO2 adsorption applications.
机译：分子模拟已成为研究晶体纳米多孔材料中气体吸附和分离的实验的重要补充。传统上，这些模拟使用力场，该力场通过将点电荷分配给吸附剂的原子来建模吸附物-孔的相互作用。框架电荷的分配总会带来歧义，因为即使定义了材料的真实电子密度，定义点电荷也有许多不同的选择。我们展示了如何通过使用根据平面波密度泛函理论（DFT）计算的静电势能面（EPES）来完全避免这种歧义。我们通过模拟四种金属有机框架（MOF）中的CO2吸附来说明这种方法：IRMOF-1，ZIF-8，ZIF-90和Zn（烟酸盐）2。所得的CO2吸附等温线对EPES的DFT计算中使用的交换相关函数不敏感，但对晶体结构和晶格参数的变化敏感。将根据DFT EPES计算的等温线与根据几种点电荷模型计算的等温线进行比较。这种比较首次使对用于描述MOF吸附的这些点电荷模型的准确性进行了无偏评估。我们发现Zn（烟酸酯）2的亨利常数（109 mmol / g·bar）和中间等规的吸附热（34.9 kj / mol）非常高，这使其成为潜在的有吸引力的CO2吸附材料。

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