Pilot applications of internally contracted multireference coupled cluster theory, and how to choose the cluster operator properly.
Pilot applications of internally contracted multireference coupled cluster theory, and how to choose the cluster operator properly.
复制标题
内契约多参考耦合聚类理论的试点应用以及如何正确选择聚类算子。
DOI：
10.1063/1.3592786
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Andreas Köhn
中科院分区：
文献类型：
--
作者：
M. Hanauer;Andreas Köhn
The internally contracted multireference coupled cluster (icMRCC) method allows a highly accurate description of both static and dynamic correlation with a computational scaling similar to single reference coupled cluster theory. The authors show that the method can lose its orbital invariance and size consistency when no special care is taken in the elimination of redundant excitations. Using the BeH(2) model system, four schemes are compared which differ in their treatment of linear dependencies between excitations of different rank (such as between singles and doubles). While the energy curves agree within tens of μE(h) when truncating the cluster operator at double excitations (icMRCCSD), inclusion of triple excitations (icMRCCSDT) leads to significant differences of more than 1 mE(h). One scheme clearly yields the best results, while the others even turn out to be not size consistent. The former procedure uses genuine single and double excitations and discards those linear combinations of (spectator) double and triple excitations which have the same effect on the reference function. With this approach, the equilibrium structure and harmonic vibrational frequencies of ozone obtained with icMRCCSDT are in excellent agreement with CCSDTQ. The authors further apply icMRCC methods to potential energy surfaces of HF, LiF, N(2), and to the singlet-triplet splitting of benzynes. In particular, the latter calculations have been made possible by implementing the method with the proper formal scaling using automated techniques.
DOI：
10.1063/1.3528720
发表时间：
2011-01
期刊：
The Journal of chemical physics
影响因子：
--
作者：
T. Shiozaki;G. Knizia;H. Werner
通讯作者：
T. Shiozaki;G. Knizia;H. Werner