Ab initio calculations of electron and nuclear spin interactions in molecules and solids using a mixed pseudopotential-all electron approach

The interaction between electronic and nuclear spins in the presence of external magnetic fields can be described by a spin Hamiltonian (SH), with parameters obtained from first principles electronic structure calculations. We previously developed an approach [1] to compute these parameters, applicable to both molecules and solids, which is based on real space density functional theory (DFT) based all-electron calculations using finite elements. Here we improve the efficiency of our approach for the calculations of spin-defects in semiconductors by combining all-electron and pseudopotential calculations: for a small region around the defect we treat explicitly all the electrons, while the rest of the crystal is described using pseudopotential calculations. We present results for the nitrogen vacancy in diamond and for divacancies in silicon carbide, including hyperfine and zero-field splitting tensors, and we show that the results of the mixed approach are in an excellent agreement with those of all-electron calculations for the full crystals. Our strategy opens the way to accurate large-scale calculations of SH parameters for the prediction of spin defect qubits in complex systems.
[1] K. Ghosh et. al. Phys. Rev. Materials 3, 2019