The open-shell coupled-cluster method: Effect of single excitations on electronic transition energies
- 15 April 1988
- journal article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 88 (8) , 5248-5249
- https://doi.org/10.1063/1.454580
Abstract
Ionization potentials (IP) of H2O and alkali atoms, excitation energies (EE) of H2O, and electron affinities (EA) of alkalies are calculated by the open-shell coupled-cluster method with double excitations only (CCD). Comparison with previously reported computations including single and double excitations (CCSD) gives the contributions of the singles. These are very small (0.02 eV) for alkali atom IPs, larger (up to 0.09 eV, or 20%) for alkali EAs, and about 0.2 eV for the water molecule IPs and EEs. One-half of the effect in water is assigned to single excitations from the closed shells.Keywords
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