Improving the Silicon Interactions of GFN-xTB

A general-purpose Density Functional Tight Binding method, the GFN-xTB model is gaining increased popularity in accurate simulations that are out of scope for conventional ab initio formalisms. We show that in its original GFN1-xTB parametrization, organosilicon compounds are described poorly. This issue is addressed by re-fitting the model's silicon parameters to a data set of ten thousand reference compounds, geometry-optimized with the revPBE functional. The resulting GFN1-xTB-Si parametrization shows improved accuracy in the prediction of system energies, nuclear forces and geometries and should be considered for all applications of the GFN-xTB Hamiltonian to systems that contain silicon.