Partially linearized, fully size-extensive, and reduced multireference coupled-cluster methods. II. Applications and performance.
Partially linearized, fully size-extensive, and reduced multireference coupled-cluster methods. II. Applications and performance.
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DOI：
10.1063/1.2868768
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发表时间：
2008-04
期刊：
影响因子：
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通讯作者：
Xiangzhu Li;J. Paldus
中科院分区：
文献类型：
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作者：
Xiangzhu Li;J. Paldus
部分线性化（pl）、完全尺寸扩展（MR）的多参考耦合簇（CC）方法，完全考虑了单重（S）和双重（D），近似考虑了一个一次比双重高的子集，称为plMR CCSD，以及它的二次三重校正的plMR CCSD（T）版本，如本文第I部分[X. Li和J. Paldus，J.Chem.Phys.128，144118（2008）]应用于HF、F2、H2O和N2分子中的键断裂问题，以及应用于H4模型，使用DZ或cc-pVDZ质量的基组，其使得能够与给定从头算模型的全构型相互作用（FCI）精确能量进行比较。在每种情况下，对plMR CCSD/CCSD（T）方法与简化MR（RMR）CCSD/CCSD（T）方法以及标准单参考（SR）CCSD和CCSD（T）方法的性能进行了比较。对于H_4模型和N_2，我们也将我们的结果与完全重整化（CR）CC（2，3）方法[P. Piecuch和M. 123，224105（2005）]。适当选择的MR型方法的模型空间的一个重要作用也得到了解决。所有这些方法的优点和缺点，指出和讨论，以及它们的尺寸扩展特性，在这种情况下，我们区分超系统涉及非相互作用SR和MR子系统只涉及MR型子系统。虽然plMR型方法呈现完全尺寸广泛的结果，而RMR CCSD可能稍微违反这一性质，后者的方法总是产生优于plMR CCSD的上级的结果，更容易应用于高要求的情况下，如氮分子中的三键断裂。
The partially linearized (pl), fully size-extensive multireference (MR) coupled-cluster (CC) method, fully accounting for singles (S) and doubles (D) and approximately for a subset of primary higher than doubles, referred to as plMR CCSD, as well as its plMR CCSD(T) version corrected for secondary triples, as described in Part I of this paper [X. Li and J. Paldus, J. Chem. Phys. 128, 144118 (2008)], are applied to the problem of bond breaking in the HF, F2, H2O, and N2 molecules, as well as to the H4 model, using basis sets of a DZ or a cc-pVDZ quality that enable a comparison with the full configuration interaction (FCI) exact energies for a given ab initio model. A comparison of the performance of the plMR CCSD/CCSD(T) approaches with those of the reduced MR (RMR) CCSD/CCSD(T) methods, as well as with the standard single reference (SR) CCSD and CCSD(T) methods, is made in each case. For the H4 model and N2 we also compare our results with the completely renormalized (CR) CC(2,3) method [P. Piecuch and M. Włoch, J. Chem. Phys. 123, 224105 (2005)]. An important role of a proper choice of the model space for the MR-type methods is also addressed. The advantages and shortcomings of all these methods are pointed out and discussed, as well as their size-extensivity characteristics, in which case we distinguish supersystems involving noninteracting SR and MR subsystems from those involving only MR-type subsystems. Although the plMR-type approaches render fully size-extensive results, while the RMR CCSD may slightly violate this property, the latter method yields invariably superior results to the plMR CCSD ones and is more easy to apply in highly demanding cases, such as the triple-bond breaking in the nitrogen molecule.