Topological analysis of the electron density distribution in perturbed systems. I. Effect of charge on the bond properties of hydrogen fluoride.
Topological analysis of the electron density distribution in perturbed systems. I. Effect of charge on the bond properties of hydrogen fluoride.
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扰动系统中电子密度分布的拓扑分析。
DOI：
10.1021/jp050776s
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
E. Molins
中科院分区：
文献类型：
--
作者：
E. Espinosa;I. Alkorta;I. Mata;E. Molins
在分子轨道 (MO) 理论的框架内，在中性 (F...H) 系统的 4sigma 反键轨道上添加一个电子或从中性 (F...H) 系统的 pi 非键合轨道中去除一个电子，形成 (F...H)- 和 (F...H)+，从而可以通过使用 rho(r) 的拓扑分析来研究这些电荷扰动对氟化氢分子键特性的影响。对于 (F...H)、(F...H)- 和 (F...H)+，在 F...H 键临界点 (BCP) 处计算的拓扑和能量性质与 3sigma 键合分子轨道 (BMO) 分布相关，因为该轨道是原子间表面 rho(r) 的主要贡献者。该分析是在几个 F...H 核间距离（范围从 0.8 到 3.0 A）进行的。就 BMO 分布而言，BMO 分布是由其与平均库仑相互作用以及由填充其他 MO 的电荷（特别是 pi 和 4sigma 电子）产生的交换电势产生的，对带电系统计算的 BCP 属性与中性系统对应的 BCP 属性之间的比较可以解释 BMO 上电荷扰动方面的差异。除了 (F...H)、(F...H)- 和 (F...H)+ 的 BCP 性质之外，还计算了相同核间距离范围内这些系统的相互作用能大小，表明所施加的扰动不会破坏 F-H 键，而是软化它，从而产生稳定的物质 (F-H)- 和 (F-H)+。比较平衡几何结构下的三个系统，最稳定的构型对应于未受扰动的 (F...H) 系统，在原子间表面显示出最高数量和最局部集中的电荷密度分布，以及最大的总电子能量密度大小，这是 BMO 向 (F...H)+ 中的氟核收缩和 BMO 向 (F...H)- 中的两个核膨胀的结果。另一方面，如果在 (F...H) (d(eq)0) 的平衡距离进行比较，则该平衡距离在原子间表面处表现出最小的总能量密度值和最大的键合电荷量。因此，作为最稳定构型的标志，中性系统 rho(d(eq)0)、倒三角形 2 rho(d(eq)0) 和 H(d(eq)0) 的特征量值在其未受扰动且松弛的电子分布的原子间表面上表现为边界条件。
Within the framework of the molecular orbital (MO) theory, the addition of one electron to the 4sigma antibonding orbital of the neutral (F...H) system or the removal of one electron from its pi nonbonding orbitals, leading to (F...H)- and to (F...H)+, has permitted the investigation of these charge perturbations on the bond properties of the hydrogen fluoride molecule by using the topological analysis of rho(r). For (F...H), (F...H)-, and (F...H)+, the topological and energetic properties calculated at the F...H bond critical point (BCP) have been related to the 3sigma bonding molecular orbital (BMO) distribution, as this orbital is the main contributor to rho(r) at the interatomic surface. The analysis has been carried out at several F...H internuclear distances, ranging from 0.8 to 3.0 A. As far as the BMO distribution results from its interaction with the average Coulomb and exchange potential generated by the charge filling the other MOs, and in particular by the pi and 4sigma electrons, the comparison between the BCP properties calculated for the charged systems and those corresponding to the neutral one permits the interpretation of the differences in terms of the charge perturbation on BMO. Along with the BCP properties of (F...H), (F...H)-, and (F...H)+, the interaction energy magnitudes of these systems have been also calculated within the same range of internuclear distances, indicating that the applied perturbations do not break the F-H bond but soften it, giving rise to the stable species (F-H)- and (F-H)+. Comparing the three systems at their equilibrium geometries, the most stable configuration, which corresponds to the unperturbed (F...H) system, shows the highest quantity and the most locally concentrated charge density distribution, along with the largest total electron energy density magnitude, at the interatomic surface as a consequence of the BMO contraction toward the fluorine nucleus in (F...H)+ and of the BMO expansion toward both nuclei in (F...H)-. On the other hand, if the comparison is carried out at the equilibrium distance of (F...H) (d(eq)0), this one exhibits both the smallest total energy density magnitude and the largest quantity of bonding charge at the interatomic surface. Hence, being the signature of the most stable configuration, the characteristic magnitudes of the neutral system rho(d(eq)0), inverted triangle2 rho(d(eq)0), and H(d(eq)0) appear as boundary conditions at the interatomic surface of its unperturbed and relaxed electron distribution.