Meissner Leszek, Musiał Monika, Kucharski Stanisław A
Institute of Physics, Nicholaus Copernicus University, Grudziadzka 5/7, 87-100 Toruń, Poland.
Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-006 Katowice, Poland.
J Chem Phys. 2020 Sep 21;153(11):114115. doi: 10.1063/5.0014941.
The single-reference coupled-cluster method has proven very effective in the ab initio description of atomic and molecular systems, but its successful application is limited to states dominated by a single Slater determinant, which is used as the reference. In cases where several determinants are important in the wave function expansion, i.e., we have to deal with nondynamic correlation effects, a multi-reference version of the coupled-cluster method is required. The multi-reference coupled-cluster approaches are based on the effective Hamiltonian formulation providing a two-step procedure, in which dynamic correlation effects can be efficiently evaluated by the wave operator, while nondynamic correlation contributions are given by diagonalization of the effective Hamiltonian in the final step. There are two classical multi-reference coupled-cluster formulations. In this paper, the focus is on the so-called Fock-space coupled-cluster method in its basic version with one- and two-particle operators in the exponent. Computational schemes using this truncation of the cluster operator have been successfully applied in calculations in one- and two-valence sectors of the Fock space. In this paper, we show that the approach can be easily extended and effectively employed in the three-valence sector calculations.
单参考耦合簇方法已被证明在从头算描述原子和分子系统方面非常有效，但其成功应用仅限于以单个斯莱特行列式作为参考的主导态。在波函数展开中几个行列式很重要的情况下，即我们必须处理非动态相关效应时，就需要耦合簇方法的多参考版本。多参考耦合簇方法基于有效哈密顿量公式，提供了一个两步过程，其中动态相关效应可以通过波算符有效评估，而非动态相关贡献则在最后一步通过有效哈密顿量的对角化给出。有两种经典的多参考耦合簇公式。本文重点关注所谓的福克空间耦合簇方法的基本版本，其指数中包含单粒子和双粒子算符。使用这种簇算符截断的计算方案已成功应用于福克空间一价和二价扇区的计算。在本文中，我们表明该方法可以很容易地扩展并有效地应用于三价扇区计算。
