Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, University of Namur, rue de Bruxelles, 61, B-5000 Namur, Belgium.
J Phys Chem A. 2013 Jun 6;117(22):4709-15. doi: 10.1021/jp403163z. Epub 2013 May 28.
The hyperpolarizabilities of three p-quinodimethane derivatives with low diradical character have been evaluated. As electron correlation effects rule the electric field response properties, wave function and density functional theory-based methods have been compared to benchmark values calculated with the coupled cluster method including single and double excitations as well as perturbative estimate of the triples [CCSD(T)]. The basis set effects have been further assessed. This study shows that the determination of the second hyperpolarizability with the CCSD method provides results in closest agreement with the CCSD(T) reference values. The use of MP2 level of theory performs well for the closed-shell compound but not for open-shell ones. Spin-projection UMP3 and UMP4 methods reproduce well UCCSD(T) values for the p-quinodimethane but not for the charged compound. Without spin projection correction, density functional theory with a large range of exchange-correlation functionals does not perform well for these systems. Similar effects have been observed for the polarizability and first hyperpolarizability, although these effects are smaller.
已评估了具有低自由基特征的三种 p-醌二亚甲基衍生物的超极化率。由于电子相关效应决定了电场响应特性，因此已将波函数和基于密度泛函理论的方法与使用耦合簇方法计算的基准值进行了比较，该方法包括单重激发和双重激发以及三重态的微扰估计[CCSD(T)]。进一步评估了基组效应。这项研究表明，使用 CCSD 方法确定二阶超极化率可提供与 CCSD(T)参考值最吻合的结果。对于闭壳化合物，MP2 理论的使用效果很好，但对于开壳化合物则不然。自旋投影 UMP3 和 UMP4 方法可很好地再现 UCCSD(T)值，适用于 p-醌二亚甲基，但不适用于带电荷的化合物。对于这些体系，没有自旋投影校正的含大范围交换相关泛函的密度泛函理论表现不佳。同样的效应也出现在极化率和一阶超极化率中，尽管这些效应较小。
