Description of non-covalent interactions in SCC-DFTB methods.

We have analyzed the description of non-covalent interactions in multiple variants of the self-consistent charges density functional tight binding (SCC-DFTB) method. While the description of London dispersion can be easily improved by empirical correction, hydrogen bonding poses a much more difficult problem. We have implemented an interaction energy decomposition scheme that allowed us to quantify the error at the level of first-order electrostatic and polarization terms. Both are underestimated because of the monopole approximation used in SCC-DFTB, with the latter being affected also by the use of minimal basis set. Among the methods tested, SCC-DFTB with the empirical D3H4 corrections worked best. To make this correction compatible with the latest development in SCC-DFTB, we have reparameterized it for use with third-order SCC-DFTB with the 3OB parameter set.