Yanai Takeshi, Chan Garnet Kin-Lic
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
J Chem Phys. 2006 May 21;124(19):194106. doi: 10.1063/1.2196410.
We propose a theory to describe dynamic correlations in bonding situations where there is also significant nondynamic character. We call this the canonical transformation (CT) theory. When combined with a suitable description of nondynamic correlation, such as given by a complete-active-space self-consistent Field (CASSCF) or density matrix renormalization group wave function, it provides a theory to describe bonding situations across the entire potential energy surface with quantitative accuracy for both dynamic and nondynamic correlation. The canonical transformation theory uses a unitary exponential ansatz, is size consistent, and has a computational cost of the same order as a single-reference coupled cluster theory with the same level of excitations. Calculations using the CASSCF based CT method with single and double operators for the potential energy curves for water and nitrogen molecules, the BeH(2) insertion reaction, and hydrogen fluoride and boron hydride bond breaking, consistently yield quantitative accuracies typical of equilibrium region coupled cluster theory, but across all geometries, and better than obtained with multireference perturbation theory.
我们提出一种理论来描述键合情形中的动态相关性，其中也存在显著的非动态特征。我们将此称为正则变换（CT）理论。当与非动态相关性的合适描述相结合时，例如由完全活性空间自洽场（CASSCF）或密度矩阵重整化群波函数给出的描述，它提供了一种理论，能够以定量精度描述整个势能面上的键合情形，包括动态和非动态相关性。正则变换理论使用酉指数假设，具有尺寸一致性，并且计算成本与具有相同激发水平的单参考耦合簇理论处于同一量级。使用基于CASSCF的CT方法，对水分子和氮分子的势能曲线、BeH(2)插入反应以及氟化氢和硼氢化物的键断裂，采用单双算符进行计算，始终能得出平衡区域耦合簇理论典型的定量精度，但适用于所有几何构型，且比多参考微扰理论得到的结果更好。
