The MCH2+ systems: do ScCH2+ and TiCH2+ have Cs or C2v symmetry and a comparison of the B3LYP method to other approaches

ScCH2+ and TiCH2+ are found to have Cs symmetry, while the remaining systems have the expected C2v symmetry. The Cs symmetry structure is favored for ScCH2+ and TiCH2+ because it allows donation from one of the CH bonds into an empty metal 3d orbital. This distortion stabilizes the systems by less than 2 kcal/mol. For V through Cu there are no empty 3d orbitals of the correct symmetry, and therefore the distortion to Cs is unfavorable. The corrected B3LYP binding energies are in good agreement with experiment and our previous best estimates.