Abstract

The electric field gradient (EFG) in hexagonal Agl at the iodine site is studied theoretically by three different procedures, namely the point charge model, the Hartree-Fock cluster approach, and the augmented plane wave band structure procedure. A comparison is made for the electronic charge distribution and the sizes of the various contributions to the EFG obtained by the different proce-dures. From the point charge model and the Hartree-Fock cluster approach one gets almost the same result for the EFG, q = +0.743 • 10 21 V/m 2 and +0.816 • 10 21 V/m 2 respectively. Only a rather preliminary result of q = +0.393 • 10 21 V/m 2 is found by the band structure calculation to be compared with the experimental value of q exp = ±0.415 • 10 21 V/m 2 . The confidence limits of the theoretical results are discussed, including possible ways to bridge the gap between the theoretical results by different methods and experiment. Both the cluster and the band structure calculations are shown to support an ionic model for hexagonal Agl with some overlap between the charge distributions on neighboring ions.