Electromagnetic nuclear shielding tensors and their relation to other second-order properties. A study of the methane molecule.

The results of an accurate calculation of second-order properties of the methane molecule are reported, with particular emphasis on dynamic shielding tensors, which enable one to evaluate the effective fields acting on the nuclei of a molecule in the presence of an electromagnetic field. The present theoretical study provides an extended numerical test, showing the reciprocal relations among different properties, i.e., sum rules and formulas explicitly linking molecular response tensors. A scheme for partitioning molecular properties into atomic contributions is discussed, which seems to imply transferability of average electric dipole polarizabilities.