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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >An Evaluation of Density Functional Theory and ab Initio Predictions for Bridge-Bonded Aluminum Compounds
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An Evaluation of Density Functional Theory and ab Initio Predictions for Bridge-Bonded Aluminum Compounds

机译：桥键铝化合物的密度泛函理论和从头算的评估

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摘要

Ab initio and density functional methods have been employed to study bridge bonding of aluminum compounds. Results for geometry optimizations and vibrational frequency calculations are found to be consistent with the recent literature. Heats of formation for the aluminum compounds dimethylaluminum hydride and trimethylaluminum are poorly described with density functional theory (DFT) methods including the hybrid DFT method. G2 calculations are closer to experimental values with estimated errors of -1.0 to -2.0 kcal/mol per Al-CH3 bond and -1.9 to -4.1 kcal/mol per A1-H bond. The major finding is that DFT methods poorly represent bridge bonding in aluminum compounds. While ab initio methods (represented by the MP2 method) reproduce experimental values within 2-3 kcal/mol, DFT methods, including the hybrid method, show errors of 5-12 kcal/mol. The DFT methods consistently under-bind the dimers of aluminum compounds with respect to two monomers. Exploration of the hybrid DFT functional shows that a better match between experiment and theory is provided by reducing the contribution of the Becke exchange correction. The binding energies are also found to be sensitive to the choice of correlation functional and the inclusion of "exact exchange". Results for associated units larger than dimers indicate it may be difficult to successfully describe all bridge-bonded aluminum compounds with existing DFT methods.
机译：从头算和密度泛函方法已用于研究铝化合物的桥键。发现几何优化和振动频率计算的结果与最新文献一致。铝化合物二甲基氢化铝和三甲基铝的形成热很难用包括混合DFT方法在内的密度泛函理论（DFT）方法描述。 G2计算更接近于实验值，每个Al-CH3键的估计误差为-1.0至-2.0 kcal / mol，每个A1-H键的估计误差为-1.9至-4.1 kcal / mol。主要发现是DFT方法不能很好地代表铝化合物中的桥键。尽管从头算方法（以MP2方法表示）在2-3 kcal / mol范围内再现了实验值，但DFT方法（包括混合方法）显示出5-12 kcal / mol的误差。 DFT方法始终将铝化合物的二聚体相对于两种单体结合不足。对混合DFT功能的探索表明，通过减少Becke交换校正的作用，可以在实验和理论之间实现更好的匹配。还发现结合能对相关功能的选择和“精确交换”的包含敏感。大于二聚体的缔合单元的结果表明，使用现有的DFT方法可能难以成功地描述所有桥键结合的铝化合物。

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