Multilevel CC2 and CCSD Methods with Correlated Natural Transition Orbitals
Multilevel CC2 and CCSD Methods with Correlated Natural Transition Orbitals
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DOI：
10.1021/acs.jctc.9b00701
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发表时间：
2020-01-01
影响因子：
5.5
通讯作者：
Koch, Henrik
中科院分区：
文献类型：
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作者：
Folkestad, Sarai Dery;Koch, Henrik
在多级耦合团簇方法中，活性轨道空间比其余的非活性轨道在耦合团簇理论的更高水平上被处理。我们介绍了多级CC 2方法，其中CC 2用于活动轨道空间。此外，我们提出了一个简化的制定的多层次CCSD方法，CCSD是用于活动空间。简化在于非活动空间中的CC 2幅度的评估;这些CC 2幅度先前已经迭代地确定。我们使用相关的自然过渡轨道来确定活动轨道空间。的收敛性的多级CC 2和多级CCSD价态激发能的概念验证计算建立。该方法也适用于两个较大的系统：对硝基苯胺在水中和阿莫西林。对对硝基苯胺-水体系的计算说明了多级耦合团簇方法对溶液中分子和电荷转移激发的有用性。
In the multilevel coupled cluster approach, an active orbital space is treated at a higher level of coupled cluster theory than the remaining inactive orbitals. We introduce the multilevel CC2 method where CC2 is used for the active orbital space. Furthermore, we present a simplified formulation of the multilevel CCSD method where CCSD is used for the active space. The simplification lies in the evaluation of the CC2 amplitudes in the inactive space; these CC2 amplitudes have previously been determined iteratively. We use correlated natural transition orbitals to determine the active orbital spaces. The convergence of the multilevel CC2 and multilevel CCSD valence excitation energies is established with proof-of-concept calculations. The methods are also applied to two larger systems: p-nitroaniline in water and amoxicillin. The calculations on the p-nitroaniline-water system illustrate the usefulness of multilevel coupled cluster methods for molecules in solution and for charge transfer excitations.