Matito Eduard, Salvador Pedro, Duran Miquel, Solà Miquel
Institut de Química Computacional and Departament de Química, Universitat de Girona, 17071 Girona, Catalonia, Spain.
J Phys Chem A. 2006 Apr 20;110(15):5108-13. doi: 10.1021/jp057387i.
In the past few years, there has been a growing interest for aromaticity measures based on electron density descriptors, the para-delocalization (PDI) and the aromatic fluctuation (FLU) indexes being two recent examples. These aromaticity indexes have been applied successfully to describe the aromaticity of carbon skeleton molecules. Although the results obtained are encouraging, because they follow the trends of other existing aromaticity measures, their calculation is rather expensive because they are based on electron delocalization indexes (DI) that involve cumbersome atomic integrations. However, cheaper electron-sharing indexes (ESIs), which in principle could play the same role as the DI in such aromaticity calculations, can be found in the literature. In this letter we show that PDI and FLU can be calculated using fuzzy-atom bond order (FBO) measures instead of DIs with an important saving of computing time. In addition, a basis-set-dependence study is performed to assess the reliability of these measures. FLU and PDI based on FBO are shown to be both good aromaticity indexes and almost basis-set-independent measures. This result opens up a wide range of possibilities for PDI and FLU to also be calculated on large organic systems. As an example, the DI and FBO-based FLU and PDI indexes have also been calculated and compared for the C60 molecule.
在过去几年中，基于电子密度描述符的芳香性度量方法越来越受到关注，对位离域化（PDI）和芳香性波动（FLU）指数就是最近的两个例子。这些芳香性指数已成功应用于描述碳骨架分子的芳香性。尽管所得结果令人鼓舞，因为它们遵循其他现有芳香性度量方法的趋势，但由于它们基于涉及繁琐原子积分的电子离域化指数（DI），其计算成本相当高。然而，文献中可以找到更便宜的电子共享指数（ESI），原则上它们在这种芳香性计算中可以起到与DI相同的作用。在这封信中，我们表明可以使用模糊原子键级（FBO）度量来计算PDI和FLU，而不是使用DI，从而显著节省计算时间。此外，还进行了基组依赖性研究，以评估这些度量的可靠性。基于FBO的FLU和PDI被证明既是良好的芳香性指数，又是几乎与基组无关的度量。这一结果为在大型有机体系上计算PDI和FLU开辟了广泛的可能性。例如，还对C60分子计算并比较了基于DI和FBO的FLU和PDI指数。
