Perturbative treatment of triple excitations in internally contracted multireference coupled cluster theory.
Perturbative treatment of triple excitations in internally contracted multireference coupled cluster theory.
复制标题
DOI：
10.1063/1.4718700
复制
发表时间：
2012-05
期刊：
影响因子：
--
通讯作者：
M. Hanauer;Andreas Köhn
中科院分区：
文献类型：
--
作者：
M. Hanauer;Andreas Köhn
基于 Dyall 的零阶哈密顿量定义，制定了对三重激励进行微扰处理的内部收缩多参考耦合簇 (ic-MRCC) 方法。迭代模型 ic-MRCCSDT-1、ic-MRCC3 及其变体 ic-MRCCSD(T)、ic-MRCC(3) 通过非迭代步骤确定三元组的能量校正，其单参考极限分别与 CCSDT-1a、CC3、CCSD(T) 和 CC(3) 一致。对BeH(2)、H(2)O和N(2)的势能面以及臭氧分子的结构和谐振频率的数值测试表明，这些方法很好地解释了高阶相关效应。 ic-MRCCSD(T)方法进一步应用于双核过渡金属氧化物Ni(2)O(2)对称振动模式的几何优化和谐波频率，邻、间和对苯炔的单重态-三重态分裂以及分子式为C(6)H(7)NO的氮丙啶化合物的开环反应。本研究中使用的活动空间的大小范围从 CAS(2,2) 到 CAS(8,8)。基于不同大小活动空间的结果比较表明，ic-MRCCSD(T) 方法提供了与最小活动空间相关的静态和动态电子关联的高度准确和有效的处理。
Internally contracted multireference coupled cluster (ic-MRCC) methods with perturbative treatment of triple excitations are formulated based on Dyall's definition of a zeroth-order Hamiltonian. The iterative models ic-MRCCSDT-1, ic-MRCC3, and their variants ic-MRCCSD(T), ic-MRCC(3) which determine the energy correction from triples by a non-iterative step are consistent in the single-reference limit with CCSDT-1a, CC3, CCSD(T), and CC(3), respectively. Numerical tests on the potential energy surfaces of BeH(2), H(2)O, and N(2) as well as on the structure and harmonic vibrational frequencies of the ozone molecule show that these methods account very well for higher order correlation effects. The ic-MRCCSD(T) method is further applied to the geometry optimization and harmonic frequencies of the symmetric vibrational modes of the binuclear transition metal oxide Ni(2)O(2), to the singlet-triplet splittings of o-, m-, and p-benzyne and to a ring-opening reaction of an azirine compound with the molecular formula C(6)H(7)NO. The size of the active spaces used in this study ranges from CAS(2,2) to CAS(8,8). Comparisons of results based on differently sized active spaces indicate that the ic-MRCCSD(T) method provides a highly accurate and efficient treatment of both static and dynamic electron correlation in connection with minimal active spaces.