Comment on ‘Theoretical calculations of the nuclear magnetic shielding tensors for the ethylenic carbon atoms in cyclopropenes’

We compare several methods for the calculation of NMR shielding tensors at the Hartree-Fock level (most of them using some sort of distributed gauge origins), applied to the 13C shielding tensors in cyclopropene C3H4 and its dichloro and tetrachloro derivatives, C3H2Cl2 and C3Cl4. Among these methods is one recently proposed by Smith et al. that in our opinion should not be called IGLO. Since multiconfiguration IGLO calculations indicate that correlation effects are important in these molecules, the quality of Hartree-Fock based methods cannot be judged from a comparison with experiment. Instead a comparison with the Hartree-Fock limit is necessary. Therefore IGLO benchmark calculations for these molecules using large basis sets are presented.