Spin-Orbit Coupling corrections for the GFN-xTB method

Spin-orbit coupling (SOC) is crucial for correct electronic structure analysis in molecules and materials, for example in large molecular systems as in superatoms, for understanding the role of transition metals in enzymes, and when investigating the energy transfer processes in metal-organic frameworks. We extend the GFN-xTB method, popular to treat extended systems, by including SOC into the hamiltonian operator. We followed the same approach as previously reported for the density-functional tight-binding (DFTB) method and provide and validate the necessary parameters for all elements throughout the periodic table. The parameters have been obtained consistently from atomic SOC calculations using density-functional theory. We tested them for reference structures where SOC is decisive, as in transition metal containing heme moiety, chromophores in metal-organic frameworks, and in superatoms. Our parametrization paves the path for incorporation of SOC in GFN-xTB based electronic structure calculations of computationally expensive molecular systems.