Spin-orbit coupling in Mo3S7(dmit)3

Spin-orbit coupling in crystals is known to lead to unusual direction-dependent exchange interactions; however understanding of the consequences of such effects in molecular crystals is incomplete. Here we perform four-component relativistic density functional theory computations on the multinuclear molecular crystal ${\mathrm{Mo}}₃{\mathrm{S}}₇$(dmit)${}₃$ and show that both intra- and intermolecular spin-orbit coupling are significant. We describe a powerful Wannier spin-orbital construction technique and use it to determine a long-range relativistic single-electron Hamiltonian from first principles. We analyze the various contributions to this Hamiltonian through the lens of group theory, building on our previous work. Intermolecular spin-orbit couplings like those found here are known to lead to quantum spin-Hall and topological insulator phases on the 2D lattice formed by the tight-binding model predicted for a single layer of ${\mathrm{Mo}}₃{\mathrm{S}}₇$(dmit)${}₃$.