Boguslawski Katharina
Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Torun, Grudziadzka 5, 87-100 Torun, Poland and Faculty of Chemistry, Nicolaus Copernicus University in Torun, Gagarina 7, 87-100 Torun, Poland.
J Chem Phys. 2016 Dec 21;145(23):234105. doi: 10.1063/1.4972053.
Wavefunctions restricted to electron pair states are promising models for strongly correlated systems. Specifically, the pair Coupled Cluster Doubles (pCCD) ansatz allows us to accurately describe bond dissociation processes and heavy-element containing compounds with multiple quasi-degenerate single-particle states. Here, we extend the pCCD method to model excited states using the equation of motion (EOM) formalism. As the cluster operator of pCCD is restricted to electron-pair excitations, EOM-pCCD allows us to target excited electron-pair states only. To model singly excited states within EOM-pCCD, we modify the configuration interaction ansatz of EOM-pCCD to contain also single excitations. Our proposed model represents a simple and cost-effective alternative to conventional EOM-CC methods to study singly excited electronic states. The performance of the excited state models is assessed against the lowest-lying excited states of the uranyl cation and the two lowest-lying excited states of all-trans polyenes. Our numerical results suggest that EOM-pCCD including single excitations is a good starting point to target singly excited states.
局限于电子对态的波函数是强关联体系很有前景的模型。具体而言，对耦合簇双激发（pCCD）近似使我们能够准确描述键解离过程以及含有多个准简并单粒子态的含重元素化合物。在此，我们使用运动方程（EOM）形式将pCCD方法扩展到激发态建模。由于pCCD的簇算符局限于电子对激发，EOM - pCCD仅能针对激发电子对态。为了在EOM - pCCD中对单激发态进行建模，我们修改了EOM - pCCD的组态相互作用近似，使其也包含单激发。我们提出的模型是研究单激发电子态的传统EOM - CC方法的一种简单且经济高效的替代方案。针对铀酰阳离子的最低激发态以及全反式多烯的两个最低激发态评估了激发态模型的性能。我们的数值结果表明，包含单激发的EOM - pCCD是针对单激发态的一个良好起点。
