Second hyperpolarizability (γ) of singlet diradical system: Dependence of γ on the diradical character
Second hyperpolarizability (γ) of singlet diradical system: Dependence of γ on the diradical character
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DOI：
10.1021/jp046322x
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发表时间：
2005-02-10
影响因子：
2.9
通讯作者：
Yamaguchi, K
中科院分区：
文献类型：
--
作者：
Nakano, M;Kishi, R;Yamaguchi, K
以具有不同两端碳-碳（C-C）键长的模型化合物对醌二甲烷（PQM）分子为对象，采用多种从头算分子轨道和密度泛函理论方法，研究了单重态双自由基体系的第二超极化率（γ）与双自由基性质（γ）的关系。基于UHF计算的双自由基性质表明，在平衡几何PQM是在一个单重基态，主要表现出醌型结构，而双自由基的字符增加两端的C-C键长。在最高水平的近似下，即使用UCCSD（T）方法和6- 31 G *+漫射p（zeta = 0.0523）基组，PQM的纵向静态γ呈现中间双自由基性质的最大值（伽马值约为0.5），而伽马值对于中间和大的双自由基特征较大（y约0.5-0.7）比小的双自由基特征（y < 0.2）更容易发生。这一特点表明，在中间和有点强的相关制度的单重态双自由基系统的y值显着增强相比，在弱相关制度。这些结果证实了一个互补的研究y的变化后扭曲乙烯。
The dependence of the second hyperpolarizability (gamma) on the diradical character (gamma) for singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon-carbon (C-C) bond lengths, by several ab initio molecular orbital and density functional theory methods. The diradical character based on UHF calculations indicates that at equilibrium geometry PQM is in a singlet ground state and primarily exhibits a quinoid structure, whereas the diradical character increases when increasing both-end C-C bond lengths. At the highest level of approximation, that is, using the UCCSD(T) method with the 6-31G*+diffuse p (zeta = 0.0523) basis set, the longitudinal static gamma of PQM presents a maximum value for intermediate diradical character (gamma approximate to 0.5) while the gamma values are larger for intermediate and large diradical character (y approximate to 0.5-0.7) than for small diradical character (y < 0.2). This feature suggests that the y values of singlet diradical systems in the intermediate and somewhat strong correlation regimes are significantly enhanced as compared to those in the weak correlation regime. These results are substantiated by a complementary study of the variation in y upon twisted ethylene.