Kowalski Karol, Hirata So, Włoch Marta, Piecuch Piotr, Windus Theresa L
William R. Wiley Environmental Molecular Sciences Laboratory, Battelle, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
J Chem Phys. 2005 Aug 15;123(7):074319. doi: 10.1063/1.2001656.
The active-space coupled-cluster (CC) and equation-of-motion (EOM) CC methods with all single and double excitations with triple excitations defined via active orbitals (CCSDt, EOMCCSDt), as implemented with TENSOR CONTRACTION ENGINE, are applied to the challenging Be3 system, which is characterized by a large number of low-lying excited states dominated by two-electron transitions and significant high-order correlation effects in the ground electronic state. It is demonstrated that the CCSDt and EOMCCSDt methods provide an excellent description of complicated electronic quasidegeneracies present in the Be3 cluster. Different strategies for defining triple excitations within the CCSDtEOMCCSDt approach are discussed.
通过张量收缩引擎实现的，包含所有单双激发以及通过活性轨道定义的三激发（CCSDt、EOMCCSDt）的活性空间耦合簇（CC）和运动方程（EOM）CC方法，被应用于具有挑战性的Be3体系，该体系的特征是存在大量由双电子跃迁主导的低激发态以及基电子态中显著的高阶相关效应。结果表明，CCSDt和EOMCCSDt方法能很好地描述Be3簇中存在的复杂电子准简并性。讨论了在CCSDt - EOMCCSDt方法中定义三激发的不同策略。
