Abstract
A configuration selection method for CI calculations is discussed and applied in which the energy lowering produced in a secular equation by the addition of a given test species to a series of dominant configurations is used as an ordering parameter. Configurations with energy lowerings below a given energy cut-off value are not included in the final secular equations but instead a method of estimating the combined effect of the neglected species on the corresponding non-selected CI results is developed. The influence of the choice of main configurations used in the selection process is given close examination as well as the importance of the MO basis employed in the treatment as a whole; in the latter case a non-iterative procedure for obtaining approximate natural orbitals for such calculations is suggested. The resulting configuration selection procedure is equally applicable to all types of electronic states in any nuclear geometry and the results of the associated CI calculations are seen to be essentially equivalent to a complete treatment in which all single- and double-excitation species with respect to aseries of dominant configurations in a given state are included.
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Senior U.S. Scientist Awardee of the Alexander von Humboldt Foundation, on leave from the Department of Chemistry, University of Nebraska.
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Buenker, R.J., Peyerimhoff, S.D. Individualized configuration selection in CI calculations with subsequent energy extrapolation. Theoret. Chim. Acta 35, 33–58 (1974). https://doi.org/10.1007/PL00020553
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DOI: https://doi.org/10.1007/PL00020553