  Diffusion Monte Carlo is one of the most accurate scalable many-body methods
for solid state systems. However, to date, spin-orbit interactions have not
been incorporated into these calcualtions at a first-principles level; only
having been applied to small systems. In this technique, we use explicitly
correlated first-principles quantum Monte Carlo calculations to derive an
effective spin-orbit model Hamiltonian. The simplified model Hamiltonian is
then solved to obtain the energetics of the system. To demonstrate this method,
benchmark studies are performed in main-group atoms and monolayer tungsten
disulfide, where high accuracy is obtained.
