New predictions for singlet-triplet gaps of substituted carbenes

Recent thermodynamic analysis by Carter and Goddard suggested the best previous ab initio predictions of substituted carbene singlet-triplet splittings were in error by 3 to 17 kcal/mol. Herein we report a new approach for correlation-consistent calculations {based on generalized valence bond with configuration interaction} which yields accurate but simple wave functions. Applying the method to the singlet-triplet splittings of CH₂, CH(SiH₃), CF₂, CCl₂, CHF, and CHCl leads to good agreement (within 3 kcal/mol) with available experimental results.