Accelerating convergence in orbital magnetization calculations through a single point formula and applications to defect EPR g-tensor fingerprints

Accurate EPR g -tensors of point defects in solids often require supercells containing hundreds to thousands of atoms to suppress defect–image interactions. In this regime, perturbative linear-response implementations can become impractical because the induced-current response is highly sensitive to Brillouin-zone sampling, typically demanding dense k -point meshes. Here we implement a single-point formulation of the converse orbital-magnetization approach for EPR g -tensor calculations in periodic systems. Relative to converse schemes based on covariant finite-difference k -derivatives, the present formulation removes the auxiliary diagonalizations at k ± q and avoids explicit k -space summations, improving both computational efficiency and numerical stability under Γ -only sampling. We validate the implementation through a benchmark set of charged and neutral defects in Si, diamond, and α -quartz, comparing against (i) the covariant converse method and (ii) linear-response calculations in QE-GIPAW and CASTEP. Using the absolute relative deviation of the principal g -tensor components from experiment as a metric, we find that the single-point scheme consistently delivers smooth, accelerated supercell-size convergence and remains stable in challenging cases with partially delocalized spin densities, where the covariant finite-difference approach can exhibit non-monotonic trends (notably for V + in Si). Overall, the single-point converse formulation provides a practical accuracy-per-cost advantage for large-scale defect EPR modeling.