DFTB+, a software package for efficient approximate density functional theory based atomistic simulations.

DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), like the density functional based tight binding (DFTB) and the extended tight binding (xTB) method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than respective ab initio methods. Based on the DFTB framework it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green’s functions and many more. DFTB+ can be used as a user-friendly standalone application as well as being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features and discuss on-going developments and possible future perspectives.