Hodecker Manuel, Rehn Dirk R, Dreuw Andreas
Interdisciplinary Center for Scientific Computing, Heidelberg University, Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany.
J Chem Phys. 2020 Mar 7;152(9):094106. doi: 10.1063/1.5142354.
Employing an intermediate state representation (ISR) approach, Hermitian second-order methods for the calculation of electronic excitation energies are presented and compared in detail. These comprise the algebraic-diagrammatic construction scheme for the polarization propagator, a hybrid second-order ISR scheme based on traditional coupled-cluster theory as well as two similar approaches based on a unitary coupled-cluster (UCC) ansatz. Although in a strict perturbation-theoretical framework all prove to be identical, differences emerge when the corresponding converged cluster amplitudes are used and depending on how the similarity-transformed UCC Hamiltonian is evaluated. The resulting excitation energies, however, do not significantly differ for systems well described by means of perturbation theory.
采用中间态表示（ISR）方法，详细介绍并比较了用于计算电子激发能的厄米二阶方法。这些方法包括极化传播子的代数图示构建方案、基于传统耦合簇理论的混合二阶ISR方案以及基于酉耦合簇（UCC）假设的两种类似方法。尽管在严格的微扰理论框架下所有方法都证明是相同的，但当使用相应的收敛簇振幅时，以及根据相似变换的UCC哈密顿量的评估方式，差异就会出现。然而，对于能用微扰理论很好描述的体系，得到的激发能并没有显著差异。
