Abstract
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), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the 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 in addition to 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 also discuss on-going developments and possible future perspectives.
Highlights
Density Functional Theory (DFT)1,2 dominates the landscape of electronic structure methods, being the usual go-to technique to model large, chemically complex systems at good accuracy
This paper describes the density functional based tight binding (DFTB)+ code,7 an open source implementation, which aims at collecting the developments of this family of methods and making them generally available to the chemical, materials, and condensed matter communities
At short-ranges, this model switches, via a Fermi-like function with a range of β, to the local atomic environment as accounted for by solving a Dyson-like selfconsistent screening equation.76 β represents a measure for the range of dynamic correlation captured by the underlying electronic structure method, so it depends on the density functional or DFTB parameterization
Summary
Density Functional Theory (DFT) dominates the landscape of electronic structure methods, being the usual go-to technique to model large, chemically complex systems at good accuracy. For larger systems and time scales, force-field models instead dominate materials and chemical modeling. Between these is the domain of semi-empirical methods, derived from approximations to Hartree– Fock or DFT based methods. Within this space, density functional based tight binding (DFTB) effectively offers a reduced complexity DFT method, being derived from a simplification of Kohn–Sham DFT to a tight binding form.. This article describes extensions to this code since its original release in 2007,8 there being a lack of a more recent overview of its features and underlying theory
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