Behavior of coupled cluster energy in the strongly correlated limit of the cyclic polyene model. Comparison with the exact results
Behavior of coupled cluster energy in the strongly correlated limit of the cyclic polyene model. Comparison with the exact results
复制标题
环状多烯模型强相关极限中耦合团簇能量的行为。
DOI：
10.1002/qua.560420111
复制
发表时间：
1992
影响因子：
2.2
通讯作者：
J. Paldus
中科院分区：
文献类型：
--
作者：
P. Piecuch;J. Cizek;J. Paldus
研究了由Pariser-Parr-Pople（PPP）和Hubbard Hamilton描述的环状多烯强关联极限中基态能量的微扰展开。重点放在第一和第二阶的贡献方面的共振积分，和性能的近似耦合对理论校正的连接四重激发（ACPQ），以及ACPTQ和ACPQ + T（ACPQ）的方法，这是两个不同版本的ACPQ近似占三激发集群，进行了研究。与ACPQ，ACPTQ，和ACPQ + T（ACPQ）的方法获得的二阶贡献，然后与最近邻海森堡哈密顿量的对角化所提供的完全相关的极限的精确结果进行比较。结果表明，所有三个耦合对理论产生消失的一阶贡献，与准确的结果。本文中考虑的环状多烯的二阶贡献的最佳结果是由ACPQ + T（ACPQ）方法提供的。在这方面，所有三个耦合对理论似乎恶化的多烯尺寸接近无穷大，尽管产生良好的能量。并与交替分子轨道法的结果进行了比较。
Perturbation expansion for the ground-state energy in the strongly correlated limit of cyclic polyenes, as described by the Pariser–Parr-Pople (PPP) and Hubbard Hamiltonians, is examined. Focus is placed on the first- and second-order contributions in terms of the resonance integral, and the performance of the approximate coupled pair theory corrected for the connected quadruple excitations (ACPQ), as well as ACPTQ and ACPQ + T(ACPQ) methods, which are two different versions of ACPQ approximately accounting for the triexcited clusters, is studied. The second-order contribution obtained with the ACPQ, ACPTQ, and ACPQ + T(ACPQ) approaches is then compared with the exact result for the fully correlated limit as provided by the diagonalization of the nearest-neighbor Heisenberg Hamiltonian. It is shown that all three coupled pair theories yield vanishing first-order contribution, in agreement with the exact result. The best result for the second-order contribution for the cyclic polyenes considered in this article is provided by the ACPQ + T(ACPQ) method. In this respect, all three coupled pair theories seem to deteriorate as the polyene size approaches infinity, in spite of yielding excellent energies. Comparison is also made with the results of alternant molecular orbital method.