Electronic structure calculations of electric field gradients (EFG) at the nuclei of the anions F-, O2-, and S2- for distorted octahedral environments representing the condensed phases of LiF, MgO, and MgS show dominant short-range corrections to the Sternheimer model. In this model, the EFG at the nucleus is proportional to that calculated from charges external to the ion with the constant of proportionality reflecting screening by the anion electron density. The short-range corrections suppress and even reverse the Sternheimer predictions and act in such a way as to damp the site specificity of the nuclear quadrupole coupling constants (NQCC) observed in magnetic resonance experiments. In contrast, the Sternheimer model is shown to describe accurately the calculated EFG at the nucleus of the Na+ cation. The physical origin of the short-range corrections is connected to the well-characterized short-range contributions to the induced dipoles and quadrupoles on ions at low-symmetry sites in the condensed phase.
- QUANTUM MAS NMR, IN-CRYSTAL POLARIZABILITY, ELECTRIC-FIELD-GRADIENT, AB-INITIO, MAGIC-ANGLE, ALKALI, POLARIZATION, PARAMETERS, SIO2, SPECTROSCOPY