Automated Repulsive Parametrization for the DFTB Method

The density-functional-based tight-binding method is an efficient scheme for quantum mechanical atomistic simulations. While the most relevant part of the chemical energies is calculated within a DFT-like scheme, a fitted correction function?the repulsive energy?is used to achieve results as close to ab initio counterparts as possible. We have developed an automatic parametrization scheme to ease the process of the repulsive energy fitting, offering a more systematic and much faster alternative to the traditional fitting process. The quality of the resulting repulsives can be tuned by selecting and weighting the fit systems and the important physical properties (energy, force, Hessian) of them. Besides driving DFT calculators in the fitting process automatically, the flexibility of our scheme also allows the usage of external data (e.g., molecular dynamics trajectories or experimental data) as a reference. Results with several elements show that our procedure is able to produce parameter sets comparable to handmade ones, yet requiring far less human effort and time.