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Phys Chem Chem Phys. 2008 Jul 28;10(28):4119-27. doi: 10.1039/b803727b. Epub 2008 Jun 5.

Benchmarking the performance of spin-component scaled CC2 in ground and electronically excited states.

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  • 1Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780, Bochum, Germany.


A generalization of the spin-component scaling and scaled opposite-spin modifications of second-order Møller-Plesset perturbation theory to the approximate coupled-cluster singles-and-doubles model CC2 (termed SCS-CC2 and SOS-CC2) is discussed and a preliminary implementation of ground and excited state energies and analytic gradients is reported. The computational results for bond distances, harmonic frequencies, adiabatic and 0-0 excitation energies are compared with experimental results to benchmark their performance. It is found that both variants of the spin-scaling increase the robustness of CC2 against strong correlation effects and lead for this method even to somewhat larger improvements than those observed for second-order Møller-Plesset perturbation theory. The spin-component scaling also enhances systematically the accuracy of CC2 for 0-0 excitation energies for pi --> pi* and n --> pi* transitions, if geometries are determined at the same level.

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