Abstract
The accuracy of extrapolation procedures in conjunction with energy-based configuration selection in CI calculations is examined. The normally high accuracy of such extrapolation can deteriorate in multireference CI calculations when configuration functions of low weight are included in the root (reference) set. This is due to the inadequacy of second-order energy contribution estimates for the very large number of discarded low-contribution functions generated as single and double excitations from the minor members of the root set. The problem may be overcome by increasing the number of configurations included in the zero-order function used for the energy contribution estimation process. Illustrative results are presented for excited states of the H2O molecule and the H2O+ ion.
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Jackels, C.F., Shavitt, I. Accuracy of energy extrapolation in multireference configuration interaction calculations. Theoret. Chim. Acta 58, 81–96 (1981). https://doi.org/10.1007/BF00550421
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DOI: https://doi.org/10.1007/BF00550421