Braïda Benoît, Galembeck Sérgio E, Hiberty Philippe C
UPMC Université Paris 06, CNRS UMR 7616 , Laboratoire de Chimie Théorique, Case Courrier 137, 4 Place Jussieu, 75252 Paris, France.
Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo , 14040-901, Ribeirão Preto - SP Brazil.
J Chem Theory Comput. 2017 Jul 11;13(7):3228-3235. doi: 10.1021/acs.jctc.7b00399. Epub 2017 Jun 21.
Ozone and its sulfur-substituted isomers are studied by means of the Breathing Orbital Valence Bond ab initio method, with the objective of estimating their controversial diradical characters. The calculated weights of the various VB structures and their individual diabatic energies are found to be consistent with each other. All 1,3-dipoles can be described in terms of three major VB structures, one diradical and two zwitterionic ones, out of the six structures, forming a complete basis. Ozone has a rather large diradical character, estimated to 44%-49%. SOO and SOS are even more diradicalar, whereas SSO and especially OSO are better described as closed-shell zwitterions. Moreover, the description of 1,3-dipoles, in terms of the three major structures, yields VB weights in full agreement with simple chemical wisdom, i.e., a diradical weight of 33% when the three structures are quasi-degenerate, and a smaller (larger) value when the diradical structure is higher (lower) in energy than the zwitterionic ones. Therefore, the VB-calculated weight of the diradical structure of a molecule qualifies itself as a quantitative measure of diradical character, and not only as an indicator of tendencies. Other definitions of the diradical character, based on molecular orbital/configuration interaction methods, are discussed.
采用呼吸轨道价键从头算方法对臭氧及其硫取代异构体进行了研究，目的是估算它们存在争议的双自由基特征。发现各种VB结构的计算权重及其各自的非绝热能量相互一致。在六种结构中，所有1,3 - 偶极子都可以用三种主要的VB结构来描述，一种是双自由基结构，两种是两性离子结构，它们构成了一个完整的基组。臭氧具有相当大的双自由基特征，估计为44% - 49%。SOO和SOS的双自由基特征更强，而SSO尤其是OSO更适合描述为闭壳两性离子。此外，用这三种主要结构来描述1,3 - 偶极子，得到的VB权重与简单的化学知识完全一致，即当三种结构近似简并时，双自由基权重为33%，当双自由基结构的能量高于（低于）两性离子结构时，该值较小（较大）。因此，分子双自由基结构的VB计算权重本身就可以作为双自由基特征的定量度量，而不仅仅是一种趋势指标。还讨论了基于分子轨道/组态相互作用方法的双自由基特征的其他定义。
