Spin-conserving and spin-flipping equation-of-motion coupled-cluster method with triple excitations

被引：102

作者：

机构：

[1] Department of Chemistry, University of Southern California, Los Angeles

来源：

| 2005年 / American Institute of Physics Inc.卷 / 123期

基金：

美国国家科学基金会;

关键词：

Equations of motion;

D O I：

10.1063/1.2006091

中图分类号：

学科分类号：

摘要：

We report the implementation of the spin-conserving and spin-flipping variants of the equation-of-motion (EOM) coupled-cluster (CC) model, which includes single and double excitations in the CC part and single, double, and triple excitations in the EOM part, i.e., EOM-CC(2,3) [Hirata, Nooijen, Bartlett, Chem. Phys. Lett. 326, 255 (2000)] for closed- and open-shell references. Inclusion of triples significantly improves the accuracy of EOM-CCSD for excitation energies (EOM-EE-CCSD) and its spin-flip (SF) counterpart, EOM-SF-CCSD, especially when the reference wave function is strongly spin-contaminated. A less computationally demanding active space variant with semi-internal triples has also been implemented. The capabilities of full and active space EOM-CC(2,3) are demonstrated by applications to C O+ and CH radicals as well as to the methylene and trimethylenemethane diradicals and the dehydro- m -xylylene triradical. © 2005 American Institute of Physics.

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