Understanding intermolecular interactions of large systems in ground state and excited state by using density functional based tight binding methods

A novel energy decomposition analysis scheme, named DFTB-EDA, is proposed based on the density functional tight-binding method (DFTB/TD-DFTB), which a semi-empirical quantum mechanical Kohn–Sham-DFT for large-scale calculations. In total interaction divided into three terms: frozen density, polarization, and dispersion. Owing to small cost of DFTB/TD-DFTB, DFTB-EDA capable analyzing intermolecular interactions in large molecular systems containing several thousand atoms with high computational efficiency. It can be used not only ground states but also excited states. Test calculations, involving S66 L7 databases, molecules, non-covalent bonding complexes their lowest states, demonstrate efficiency, usefulness, capabilities DFTB-EDA. Finally, limits are pointed out.