Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Chem Phys. 2013 Jun 28;138(24):244306. doi: 10.1063/1.4810860.
The static first and second hyperpolarizabilities (referred to as β and γ, respectively) of asymmetric open-shell singlet systems have been investigated using the asymmetric two-site diradical model within the valence configuration interaction level of theory in order to reveal the effect of the asymmetric electron distribution on the diradical character and subsequently on β and γ. It is found that the increase of the asymmetric electron distribution causes remarkable changes in the amplitude and the sign of β and γ, and that their variations are intensified with the increase of the diradical character. These results demonstrate that the asymmetric open-shell singlet systems with intermediate diradical characters can exhibit further enhancements of β and γ as compared to conventional asymmetric closed-shell systems and also to symmetric open-shell singlet systems with intermediate diradical characters.
采用价层组态相互作用理论中的不对称双自由基模型，研究了不对称开壳层单线态体系的静态第一和二阶超极化率（分别称为β和γ），以揭示不对称电子分布对双自由基特性以及随后对β和γ的影响。结果发现，不对称电子分布的增加导致β和γ的幅度和符号发生显著变化，并且随着双自由基特性的增加，其变化加剧。这些结果表明，与传统的不对称闭壳层体系以及具有中等双自由基特性的对称开壳层单线态体系相比，具有中等双自由基特性的不对称开壳层单线态体系可以进一步增强β和γ。
