Long-range effects of interatomic interactions on NMR shielding constants

The effect of the weak long-range interaction on the shielding constant is considered for a pair of interacting atoms. The asymptotic long-range effects are proportional to R−n (where R is the interatomic distance). For the anisotropy of the shielding tensor n = 3, for the trace n = 6 for two neutral atoms and n = 4 for the atom shielding in an atom-ion pair. Calculations on the He-He system, using a full-CI expansion and on the Ar-Na+ interaction, using an SCF wavefunction, confirm the expected long-range dependence of the change in the shielding constant.