von Szentpály László
Institut für Theoretische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
J Phys Chem A. 2015 Mar 5;119(9):1715-22. doi: 10.1021/jp5084345. Epub 2014 Nov 6.
The strict Wigner-Witmer symmetry constraints on chemical bonding are shown to determine the accuracy of electronegativity equalization (ENE) to a high degree. Bonding models employing the electronic chemical potential, μ, as the negative of the ground-state electronegativity, χ(GS), frequently collide with the Wigner-Witmer laws in molecule formation. The violations are presented as the root of the substantially disturbing lack of chemical potential equalization (CPE) in diatomic molecules. For the operational chemical potential, μ(op), the relative deviations from CPE fall between -31% ≤ δμ(op) ≤ +70%. Conceptual density functional theory (cDFT) cannot claim to have operationally (not to mention, rigorously) proven and unified the CPE and ENE principles. The solution to this limitation of cDFT and the symmetry violations is found in substituting μ(op) (i) by Mulliken's valence-state electronegativity, χ(M), for atoms and (ii) its new generalization, the valence-pair-affinity, α(VP), for diatomic molecules. Mulliken's χ(M) is equalized into the α(VP) of the bond, and the accuracy of ENE is orders of magnitude better than that of CPE using μ(op). A paradigm shift replacing the dominance of ground states by emphasizing valence states seems to be in order for conceptual DFT.
结果表明，严格的维格纳-维特默对称性约束对化学键合具有高度的电负性均衡（ENE）准确性的决定性作用。采用电子化学势μ作为基态电负性χ(GS)的负值的键合模型，在分子形成过程中经常与维格纳-维特默定律相冲突。这些冲突表现为双原子分子中严重干扰化学势均衡（CPE）缺失的根源。对于操作化学势μ(op)，与CPE的相对偏差在-31%≤δμ(op)≤+70%之间。概念密度泛函理论（cDFT）无法宣称在操作上（更不用说严格地）证明并统一CPE和ENE原理。cDFT这一局限性以及对称性违反问题的解决方案在于，对于原子，用穆利肯价态电负性χ(M)替代μ(op)；对于双原子分子，用其新的推广形式——价对亲和力α(VP)替代μ(op)。穆利肯的χ(M)均衡为键的α(VP)，且使用ENE的准确性比使用μ(op)的CPE高出几个数量级。对于概念性DFT而言，似乎需要进行一场范式转变，从强调基态的主导地位转向强调价态。
