Nuclear electric shielding and its connections with other second-order properties

It is shown that the electric shielding tensor of a nucleus within a molecule is related to the polarisability of the corresponding atom. The condition for the electrostatic equilibrium, satisfied by the nuclear shieldings, is the Thomas-Reiche-Kuhn sum rule, and a gauge-invariance condition for the magnetisability. These achievements suggest that a unitary and synthetic theoretical framework for electric and magnetic second-order properties can be built up, where the nuclear electric shielding concept plays a major role.