DFTB+ is an implementation of the Density Functional Tight Binding (DFTB) method, containing many extensions to the original method. The development is supported by various groups, resulting in a code which is probably the most versatile DFTB-implementation, with some unique features not available in other implementations so far.
DFTB+ offers an approximate density functional theory based quantum simulation tool with functionalities similar to ab initio quantum mechanical packages while being one or two orders of magnitude faster. You can optimize the structure of molecules and solids, you can extract one electron spectra, band structures and various other useful quantities. Additionally, you can calculate electron transport under non-equilibrium conditions.
If you publish results obtained with the DFTB+ code, we ask you to cite following works:
DFTB+ paper (describing the code)
Reference publications of the Slater-Koster parameterisation set(s) you use. You find the list of those publications on the download page of the parameters and also in the parameterization files itself.
Methodological papers relevant to your calculations (e.g. excited states, electron-transport, third order DFTB etc.). Those references can be found in the DFTB+ manual.