Gradient corrections in first-principles calculations of hyperfine parameters in semiconductors

The spin-polarized density-functional method with a plane-wave basis set is used to investigate the microscopic structure and, in particular, the hyperfine parameters of hydrogenlike impurities in silicon and diamond. Both the bond-centered and the tetrahedral interstitial impurity sites are investigated. These electronic-structure calculations are performed on a highly converged level in terms of the supercell size and the quality of the basis set. The magnitudes of the spin densities at the impurity are underestimated by the local-density approximation. However, with exception of the next-nearest-neighbor Fermi contact term, further study using gradient corrections in the exchange-correlation energy and accounting for the zero-point motion of the impurity yields hyperfine parameters that are in very good agreement with the experimental values.