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用 LEMAO-3G 基组计算苯分子,优选轨道指数调节因子时,考虑到π键和σ键的差异而将ζ_(C2π)和ζ_(C2π)分开优选,得到苯的最佳调节因子组为:ζ(H1S)=1.26,ζ_(C1S)=1.0039,ζ_(C2π)=1.00761,ζ_(C2σ)=1.1043。据此算得苯分子的总能量为-229.167274a.u.,维里系数为1.00000。所得各价轨道的能量和 ESCA 数据基本相符,并与 Fischer-Hjalmars 等很接近于 Hartree-Fock 极限的计算值颇一致,而所用基组则和他们不同.分析上述结果可知:苯的芳香稳定性的原因,不仅在于其环形共轭体系中的离域作用,与之相对立而又相联系的诸轨道“收缩”或“定域”效应也起重大作用.而且σ轨道的离域与定域在其中起着比π轨道更大的作用.当σ-轨道因“动能压力”减小而显著收缩时,π电子轨道仅发生微小的收缩而呈较σ电子更弥散的状态.这一方面使π电子有较大的总能量,因而能很好地传递电子效应;另一方面使σ电子总能量降低更多,从而使苯分子总体有较大稳定性.
When calculating the benzene molecule, preferably the orbital index modifier, using the LEMAO-3G basis set, it is preferable to separate ζ_ (C2π) and ζ_ (C2π) from the difference between the π bond and the σ bond to obtain the optimal set of adjustment factors for benzene as: ζ (H1S) = 1.26, ζ_ (C1S) = 1.0039, ζ_ (C2π) = 1.00761, ζ_ (C2σ) = 1.1043. Based on this calculation, the total energy of the benzene molecule is -229.167274 a.u., and the virial coefficient is 1.00000. The energies of the orbitals obtained are basically consistent with those of the ESCA data and are consistent with the calculated values close to the Hartree-Fock limit of the Fischer-Hjalmars et al. The basis sets used are different from those of the ESCA data. Analyzing the above results shows that the benzene aromatic stability Is not only due to the delocalization in its circular conjugated system, but also plays an important role in the “contraction” or “localization” effect of the orbits which are opposite to each other and the delocalization and localization In which plays a greater role than the π orbit when π-orbit due to the “kinetic pressure” decreased significantly contracted, π electron orbit only minor shrinkage occurs more diffuse than the σ electron state on the one hand π electron has a larger total energy, which can well transfer the electronic effect; the other hand, the total energy of σ electron to reduce more, so that benzene molecules generally have greater stability.