Pseudopotential hyperfine calculations through perturbative core-level polarization

Within density functional theory, an efficient and accurate method for calculating the hyperfine parameters in the context of pseudopotential formalism is proposed. The spin density at and in the vicinity of the nucleus is evaluated in two steps. First, a transformation due to Blöchl [Phys. Rev. B 50, 17953 (1994)] is applied to reconstruct the frozen-core all-electron wave functions in the core regions. Second, the contributions of core orbitals to the charge density at the nucleus are evaluated through first-order perturbation theory in which the perturbing potential is defined as a functional of charge and spin densities. The current pseudopotential based method makes it possible to predict hyperfine parameters of complex molecular assemblies and crystal defects with an accuracy as good as current all-electron method with less computational cost.