with the potential V being approximated as Van Wüllen's model potential. c is the speed of light and p = -i∇ the momentum operator matrix. σ P represents the vector of Pauli spin matrices. Final resulting couplings between singlet and triplet states of different spin quantum numbers are given in the supplementary information. Alternatively, if restricting the description to valence electrons only, a SOC-corrected pseudopotential, as parameterized by Hartwigsen et al. , can be used,