Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
J Chem Phys. 2011 Jan 14;134(2):024114. doi: 10.1063/1.3526066.
A new parameterization for the Pariser-Parr-Pople (PPP) model for conjugated hydrocarbons is proposed in this work. The distance-dependence of PPP parameters are obtained from CASPT2 ground state and low-lying excited state energies of ethylene and its cation at various C-C single bond lengths and are fitted to a set of carefully chosen mathematical functions. Our new PPP model is applied to the calculation of vertical singlet-triplet energy gaps and the excitation energies for low-lying π→π(*) valence excitations in various π-conjugated molecules. Results with the new PPP model are consistently better than the standard PPP model in use. It often surpasses density functional theory and single-reference excited state methods such as configuration interaction singles or time-dependent density functional theory in terms of its accuracy and agrees reasonably well with high-level theories or experiments.
本文提出了一种新的共轭烃 Pariser-Parr-Pople（PPP）模型参数化方法。该方法通过 CASPT2 方法计算了乙烯及其阳离子在不同 C-C 单键长度下的基态和低能激发态能量，得到了 PPP 参数的距离依赖性，并将其拟合到一组精心选择的数学函数中。我们的新 PPP 模型应用于计算各种π-共轭分子的垂直单重态-三重态能隙和低能π→π(*)价激发的激发能。与标准 PPP 模型相比，新 PPP 模型的计算结果更加准确。在准确性方面，它通常优于密度泛函理论和单参考激发态方法，如组态相互作用单激发或时变密度泛函理论，并且与高精度理论或实验结果吻合良好。
