First-principles calculations of interlayer magnetic couplings in Kitaev spin-liquid candidate alpha-RuCl3

We use density functional theory, the constrained random phase approximation, Wannier functions and strong coupling perturbation theory to derive the out-of-plane magnetic interactions in C2/m and R3bar alpha-RuCl3 and compare our results against inelastic neutron scattering experiments. We quantify the magnetic two-dimensionality of alpha-RuCl3 that is crucial for its potential to host anyons. Furthermore, our calculations are relevant for the reported sensitivity of the half-integer quantum thermal Hall effect to the interlayer structure of this Kitaev spin-liquid candidate material.