The SCC-DFTB method and its application to biological systems

The Self-consistent charge density functional tight-binding (SCC-DFTB) is an approximate quantum chemical method derived from density functional theory (DFT) based on a second-order expansion of the DFT total energy expression. Here, we review in detail the application of SCC-DFTB to biological systems and several extensions of the original formalism. The biological systems discussed turn out to be a challenge for DFT due to the occurrence of weak binding forces and charge transfer problems, both of which are not properly described by recent DFT-GGA functionals. Possible solutions and alternative strategies are presented and the role of SCC-DFTB in a general quantum chemical approach to biological systems is discussed.