Haldar Soumi, Mukhopadhyay Tamoghna, Dutta Achintya Kumar
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
J Chem Phys. 2022 Jan 7;156(1):014110. doi: 10.1063/5.0064889.
We present a novel and cost-effective approach of using a second similarity transformation of the Hamiltonian to include the missing higher-order terms in the second-order approximate coupled cluster singles and doubles (CC2) model. The performance of the newly developed ST-EOM-CC2 model has been investigated for the calculation of excitation energies of valence, Rydberg, and charge-transfer excited states. The method shows significant improvement in the excitation energies of Rydberg and charge-transfer excited states as compared to the conventional CC2 method while retaining the good performance of the latter for the valence excited state. This method retains the charge-transfer separability of the charge-transfer excited states, which is a significant advantage over the traditional CC2 method. A second order many-body perturbation theory variant of the new method is also proposed.
我们提出了一种新颖且经济高效的方法，即利用哈密顿量的第二次相似变换，将缺失的高阶项纳入二阶近似耦合簇单双激发（CC2）模型。针对价态、里德堡态和电荷转移激发态的激发能计算，研究了新开发的ST-EOM-CC2模型的性能。与传统CC2方法相比，该方法在里德堡态和电荷转移激发态的激发能计算上有显著改进，同时在价态激发态方面保留了传统CC2方法的良好性能。该方法保留了电荷转移激发态的电荷转移可分离性，这是相对于传统CC2方法的一个显著优势。还提出了该新方法的二阶多体微扰理论变体。
