Abstract
Multiple perturbation theory is used to calculate the response of the electric field gradient at the nucleus of the hydrogen atom to external non-uniform fields. The parallel component of the field gradient at the nucleus in an axial field F with gradient F′ and second derivative F″ has the perturbation expansion:
For perturbations by a distant charge the terms of order R -4 and R -6 are reinforcing and combine to oppose the Sternheimer shielding which contributes at order R -3. Symmetry considerations for the general atomic case are discussed.