Iterative and non-iterative triple excitation corrections in coupled-cluster methods for excited electronic states: the EOM-CCSDT-3 and EOM-CCSD(T̃) methods
✍ Scribed by John D. Watts; Rodney J. Bartlett
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 532 KB
- Volume
- 258
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
New iterative and non-iterative triple excitation corrections to EOM-CCSD are presented based upon the CCSDT-3 method. This method is recommended formally, since it fully employs the EOM-CCSD Hamiltonian /t = exp[-(T 1 + T2)]H exp(T I + T z) in its development. This permits defining iterative EOM-CCSDT-3 and non-iterative EOM-CCSD('F) corrections correct through second-order in /4. Results for some full CI examples demonstrate average errors of 0.09 eV and 0.08 eV, respectively. We also study trans-butadiene as a more demanding example. We also consider a computationally simpler but accurate approximation to EOM-CCSD(q'), EOM-CCSD(T').