CALCULATION OF ELECTRIC HYPERFINE INTERACTION PARAMETERS IN SOLIDS

A theoretical approach for the calculation of hyperfine parameters in solids from first principles is presented. These calculations are base d on the full potential linearized-augmented-plane-wave (LAPW) band st ructure method, which is currently one of the most accurate schemes to determine the electronic structure in ordered solids. Exchange and co rrelation is treated within density functional theory using the genera lized gradient approximation. Once the electron density is calculated self-consistently with high accuracy, quantities like electric field g radients (EFG), isomer shifts or hyperfine fields can easily be obtain ed from this density without further approximations. Using this approa ch we have studied various systems including metals, insulators, ionic compounds or the high T-c superconductors. In general we find good ag reement between theory and experiment, which proves that our method is very accurate. Having these results in mind we are confident that thi s method is accurate enough to determine the value of the nuclear quad rupole moment Q, provided experimental measurements of the quadrupole coupling constant are available. This procedure is demonstrated for Q of Se-77 and Rh-100, two nuclei recently used in PAC measurements. An extensive study of EFGs at Fe sites in various Fe-compounds has been p erformed leading to a very reliable quadrupole moment of Q(Fe-57) = 0. 16 b, a value twice as large as that deduced from recent HF calculatio ns but back to older estimates.