GENERALIZED-MOLECULAR-ORBITAL THEORY - SIMPLE MULTICONFIGURATION SELF-CONSISTENT-FIELD METHOD
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AbstractEven after completing a multiconfiguration selfconsistentfield (MCSCF) calculation, one must often include additional configuration interaction (CI) to obtain quantitative or semiquantitative results. There is some question of whether the prior MCSCF calculation is worthwhile, if additional CI is needed later. We have developed a new MCSCF computational method, which, because of our assumptions about the nature of the configurations, yields one Focklike operator for all the filled orbitals (high occupation numbers) and a second Focklike operator for all the virtual orbitals (low occupation numbers). Since there are only two matrices to build, our method is considerably faster than other MCSCF approaches. Because of these similarities to standard molecularorbital (MO) calculations, we have termed our approach generalizedmolecularorbital (GMO) theory. However, the virtual orbitals, unlike those of standard MO theory, are optimized to correlate the filled ones and can he used in a subsequent CI calculation. Results are presented for the correlation energy of H2O, the spectroscopic constants of N2, the singlettriplet energy separations in CH2, and the nature of the chromiumchromium quadruple bond. Although these results are at a very low level of CI, the GMO approach appears to correct for the gross deficiencies of the singledeterminant SCF procedure.
