Scalar relativistic calculations of hyperfine coupling tensors using the Douglas–Kroll–Hess method

Scalar relativistic calculations of hyperfine coupling tensors have been implemented for the first time at the Douglas–Kroll–Hess level, with proper transformation of hyperfine operators up to second order. Implementation into the ReSpect program has allowed the assessment of the new approach for a number of atoms and diatomic molecules, in comparison with experimental data and other calculations. While neglect of the transformation of the operators leads to meaningless hyperfine results, DFT calculations with operators transformed to first order agree already relatively well with previous ZORA results. Full transformation to second order leads to larger isotropic hyperfine couplings.