Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44801 Bochum, Germany.
J Chem Phys. 2018 Apr 7;148(13):134102. doi: 10.1063/1.5018514.
We present a pair natural orbital (PNO)-based implementation of coupled cluster singles and doubles (CCSD) excitation energies that builds upon the previously proposed state-specific PNO approach to the excited state eigenvalue problem. We construct the excited state PNOs for each state separately in a truncated orbital specific virtual basis and use a local density-fitting approximation to achieve an at most quadratic scaling of the computational costs for the PNO construction. The earlier reported excited state PNO construction is generalized such that a smooth convergence of the results for charge transfer states is ensured for general coupled cluster methods. We investigate the accuracy of our implementation by applying it to a large and diverse test set comprising 153 singlet excitations in organic molecules. Already moderate PNO thresholds yield mean absolute errors below 0.01 eV. The performance of the implementation is investigated through the calculations on alkene chains and reveals an at most cubic cost-scaling for the CCSD iterations with the system size.
我们提出了一种基于对映轨道（PNO）的耦合簇单双激发能的实现方法，该方法基于先前提出的针对激发态特征值问题的态特定 PNO 方法。我们分别在截断的轨道特定虚拟基中为每个态构建激发态 PNO，并使用局部密度拟合近似来实现 PNO 构建的计算成本最多为二次方的缩放。早期报告的激发态 PNO 构建被推广，从而确保了一般耦合簇方法对电荷转移态的结果的平滑收敛。我们通过将其应用于包含 153 个有机分子中单重激发的大型和多样化测试集来研究我们的实现的准确性。已经适度的 PNO 阈值产生低于 0.01eV 的平均绝对误差。通过对烯烃链的计算来研究实现的性能，并揭示了与系统大小相比，CCSD 迭代的成本最多为三次方的成本缩放。
