Magoulas Ilias, Bauman Nicholas P, Shen Jun, Piecuch Piotr
Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States.
Department of Physics and Astronomy, Michigan State University , East Lansing, Michigan 48824, United States.
J Phys Chem A. 2018 Feb 8;122(5):1350-1368. doi: 10.1021/acs.jpca.7b10892. Epub 2018 Jan 30.
The performance of coupled-cluster approaches with higher-than-doubly excited clusters, including the CCSD(T), CCSD(2), CR-CC(2,3), CCSD(TQ), and CR-CC(2,4) corrections to CCSD, the active-space CCSDt, CCSDtq, and CCSDTq methods, and the CC(t;3), CC(t,q;3), CC(t,q;3,4), and CC(q;4) corrections to CCSDt, CCSDtq, and CCSDTq resulting from the CC(P;Q) formalism, in reproducing the CCSDT and CCSDTQ potential energy curves and vibrational term values characterizing Be in its electronic ground state is assessed. The correlation-consistent aug-cc-pVnZ and aug-cc-pCVnZ (n = T and Q) basis sets are employed. Among the CCSD-based corrections, the completely renormalized CR-CC(2,3) and CR-CC(2,4) approaches perform the best. The CC(t;3), CC(t,q;3), CC(t,q;3,4), and CC(q;4) methods, especially CC(t;3) and CC(q;4), outperform other employed approaches in reproducing the CCSDT and CCSDTQ data. Composite schemes combining the all-electron CCSDT calculations extrapolated to the complete basis set limit with the frozen-core CC(q;4) and CCSDTQ computations using the aug-cc-pVTZ basis to account for connected quadruple excitations reproduce the latest experimental vibrational spectrum of Be to within 4-5 cm, when the vibrational spacings are examined, with typical errors being below 1-2 cm. The resulting binding energies and equilibrium bond lengths agree with their experimentally derived counterparts to within ∼10 cm and 0.01 Å.
评估了包含对CCSD的CCSD(T)、CCSD(2)、CR-CC(2,3)、CCSD(TQ)和CR-CC(2,4)修正、活性空间CCSDt、CCSDtq和CCSDTq方法，以及由CC(P;Q)形式主义对CCSDt、CCSDtq和CCSDTq产生的CC(t;3)、CC(t,q;3)、CC(t,q;3,4)和CC(q;4)修正的高于双激发簇的耦合簇方法，在再现表征处于电子基态的Be的CCSDT和CCSDTQ势能曲线及振动项值方面的性能。使用了相关一致的aug-cc-pVnZ和aug-cc-pCVnZ（n = T和Q）基组。在基于CCSD的修正中，完全重整化的CR-CC(2,3)和CR-CC(2,4)方法表现最佳。CC(t;3)、CC(t,q;3)、CC(t,q;3,4)和CC(q;4)方法，特别是CC(t;3)和CC(q;4)，在再现CCSDT和CCSDTQ数据方面优于其他所采用的方法。将外推到完全基组极限的全电子CCSDT计算与使用aug-cc-pVTZ基组考虑连接四重激发的冻结核心CC(q;4)和CCSDTQ计算相结合的复合方案，在检查振动间距时，将Be的最新实验振动光谱再现到4 - 5 cm以内，典型误差低于1 - 2 cm。由此得到的结合能和平衡键长与通过实验得出的对应值在约10 cm和0.01 Å范围内相符。
