High-quality DFTB parameters allow a near-1:1 reproduction of molecular orbital (MO) electronic energy levels for molecules, as well as valence and conduction band structures for bulk solid materials relative to DFT . Repulsive potentials can be optimized such that DFTB calculations are able to reproduce DFT geometrical parameters as well as vibrational and optical spectra. In terms of computational accuracy and efficiency, DFTB is settled in between traditional DFT methods and classical force field approaches, although higher accuracy than DFT can be achieved at times when empirical data is employed in the parameterization, for instance for the prediction of band gaps .