Kjønstad Eirik F, Angelico Sara, Koch Henrik
Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Department of Chemistry, Stanford University, Stanford, California 94305, United States.
J Chem Theory Comput. 2024 Aug 13;20(16):7080-92. doi: 10.1021/acs.jctc.4c00276.
Coupled cluster theory is one of the most accurate electronic structure methods for predicting ground and excited state chemistry. However, the presence of numerical artifacts at electronic degeneracies, such as complex energies, has made it difficult to apply the method in nonadiabatic dynamics simulations. While it has already been shown that such numerical artifacts can be fully removed by using similarity constrained coupled cluster (SCC) theory [ (19), 4801-4807], simulating dynamics requires efficient implementations of gradients and nonadiabatic couplings. Here, we present an implementation of nuclear gradients and nonadiabatic derivative couplings at the similarity constrained coupled cluster singles and doubles (SCCSD) level of theory, thereby making possible nonadiabatic dynamics simulations using a coupled cluster theory that provides a correct description of conical intersections between excited states. We present a few numerical examples that show good agreement with literature values and discuss some limitations of the method.
耦合簇理论是预测基态和激发态化学性质最精确的电子结构方法之一。然而，在电子简并处存在数值伪影，如复能量，这使得该方法难以应用于非绝热动力学模拟。虽然已经表明，通过使用相似性约束耦合簇（SCC）理论[（19），4801 - 4807]可以完全消除此类数值伪影，但模拟动力学需要高效实现梯度和非绝热耦合。在此，我们展示了在相似性约束耦合簇单双激发（SCCSD）理论水平下核梯度和非绝热导数耦合的实现，从而使得使用能够正确描述激发态之间锥形交叉的耦合簇理论进行非绝热动力学模拟成为可能。我们给出了一些与文献值吻合良好的数值示例，并讨论了该方法的一些局限性。
