Hyperfine Interactions for Small Molecules using Fermi-Löwdin Orbital Based Self-Interaction Corrected DFT

Hyperfine interactions play an important role in characterizing electronic structure using EPR or NMR, as well as in designing qubit systems. The major component of the hyperfine interaction energy, the Fermi-contact (FC) term, is proportional to the electron spin density at the nuclear position. The FC term tends to be significantly underestimated in density-functional theory (DFT) methods due to self-interaction errors (SIE), arising from approximate exchange-correlation functionals, which results in significant electron- and spin-density delocalization. A recently developed self-interaction correction (SIC) method is based on Fermi-Löwdin orbitals (FLO), which depend on the positions of Fermi-Orbital Descriptors (FODs). The FLO-SIC method has been successfully applied to various systems; however, its performance for the FC term has not been assessed yet. We carried out FLO-SIC calculations on small transition metal-based molecules and computed the FC term in each case. The starting set of FODs for each calculation was generated using the symmetries of the system, as well as the Lewis structures predicted with natural bond orbital theory. The results from the FLO-SIC method are compared with those from the SIC-free generalized-gradient approximation method and experiments.