Full CI calculations are presented for the1A1,3B1, and1B1states of SiH2at their respective equilibrium geometries and at geometries with the SiH bonds stretched. These results are compared with those obtained from single reference and multireference CI calculations. The computedTevalues agree well with the full CI results provided that the effects of higher than double excitations are accounted for either by the Davidson correction or by a multireference approach. When the SiH bonds are stretched the single reference methods are not sufficiently flexible, and only CASSCF/MRCI achieves chemical accuracy (i.e., agrees with the full CI to 1 kcal/mol). Overall, the accuracy of the various approximate methods is very similar to that found for H2O, NH2, and CH2.
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