Department of Chemistry , Norwegian University of Science and Technology , 7491 Trondheim , Norway.
Scuola Normale Superiore , Piazza dei Cavalieri, 7 , 56126 Pisa , Province of Pisa , Italy.
J Chem Theory Comput. 2019 Oct 8;15(10):5386-5397. doi: 10.1021/acs.jctc.9b00702. Epub 2019 Sep 20.
We present a similarity constrained coupled cluster method able to describe conical intersections between two excited electronic states of the same symmetry. For a given pair of states, this singles and doubles method (SCCSD) is unique and orbital invariant. The computational cost scales as the sixth power with respect to the number of orbitals, and preliminary calculations indicate that the excitation energy difference relative to CCSD is within the error range of CCSD (approximately 0.10 eV). We also analyze the size-scaling properties of the orthogonality condition. For a projected orthogonality condition we show, and demonstrate numerically, that the method is rigorously size-intensive.
我们提出了一种相似性约束的耦合簇方法，能够描述相同对称性的两个激发电子态之间的交叉。对于给定的一对态，这种单激发和双激发方法（SCCSD）是独特的且轨道不变的。该方法的计算成本与轨道数的六次方成正比，初步计算表明，与 CCSD 相比，激发能差在 CCSD 的误差范围内（约 0.10 eV）。我们还分析了正交条件的大小缩放性质。对于投影正交条件，我们证明并通过数值演示了该方法是严格的大小密集型的。
