Abstract
We use the constrained random phase approximation to derive from first principles the Ru-t2g Wannier-function-based model for the Kitaev spin-liquid candidate material α−RuCl3. We find the nonlocal Coulomb repulsion to be sizable compared to the local one. In addition we obtain the contribution to the Hamiltonian from the spin-orbit coupling and find it to also contain non-negligible nonlocal terms. We invoke strong-coupling perturbation theory to investigate the influence of these nonlocal elements of the Coulomb repulsion and the spin-orbit coupling on the magnetic interactions. We find that the nonlocal Coulomb repulsions cause a strong enhancement of the magnetic interactions, which deviate from experimental fits reported in the literature. Our results contribute to the understanding and design of quantum spin-liquid materials via first-principles calculations.
