Applications of level shift corrected perturbation theory in electronic spectroscopy
Roos, BO × Andersson, K Fulscher, MP SerranoAndres, L Pierloot, Kristine Merchan, M Molina, V #
Elsevier Scientific Pub. Co.
Journal of Molecular Structure. Theochem vol:388 pages:257-276
Multiconfigurational second-order perturbation theory (CASPT2) with a level shift technique used to reduce the effect of intruder states has been tested for applications in electronic spectroscopy. The following molecules have been studied: formamide, adenine, stilbene, Ni(CO)(4), and a model compound for the active site in the blue copper protein plastocyanin, Cu(Im)(2)(SH)(SH2)(+). The results show that the level shift technique can be used to remove the effects of the intruder states in all these molecules. In some cases a drift in the energies as a function of the level shift is observed, which however is small enough that the normal error bar for CAsPT2 excitation energies (approximate to 0.3 eV) still holds.