Tight-Binding DFT for Molecular Electronics (gDFTB)

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We present a detailed description of the implementation of the nonequilibrium Green’s function technique on the density-functional-based tightbinding simulation tool (gDFTB). This approach can be used to compute electronic transport in organic and inorganic molecular-scale devices. The tight-binding formulation gives an efficient computational tool able to handle a large number of atoms. The non-equilibrium Green’s functions are used to compute the electronic density self-consistently with the open-boundary conditions naturally encountered in transport problems and the boundary conditions imposed by the potentials at the contacts. The Hartree potential of the density-functional Hamiltonian is obtained by solving the three-dimensional Poisson’s equation involving the non-equilibrium charge density. This method can treat, within a unified framework, coherent and incoherent transport mechanisms.