To perform practical calculations, approximations are necessary. There are theorems that guarantee its solid foundation as an exact theory, in principle. One could say that DFT is today the standard approach for ab initio electronic structure calculations of medium to large systems, including molecules, bulk solids, surfaces, nano-systems, etc. Albeit with some drawbacks, as discussed later on, the Density Functional Theory Non-Equilibrium Green's Function (DFT-NEGF) approach to charge transport calculations comes very close to satisfying a good number of these requirements. Even though many fundamental concepts related to the understanding of how charge flows in such small systems are already well established, there are still quite a few challenges if one wants to quantitatively calculate a property such as an I × V curve.Īny theory with this predictive power should obey a number of requirements: i) a reliable description of the electronic structure properties of the atoms in the scattering region ii) the treatment of the leads in the same footing as the scattering region iii) it should have no adjustable parameters iv) the self-consistent calculation of the charge redistribution within the scattering region due to the application of a voltage bias v) it should do all this for a variety of different systems. All these systems have the same basic physical picture, with a central scattering region connected to a certain number of leads. In the past few years it has been possible to measure the charge transport across nanometric systems, such as carbon nanotubes, metallic nanowires, and molecules. Keywords: Charge Transport Density Functional Theory Non-Equilibrium Green's Function As an illustration, we perform calculations for the charge transport across a (5,5) carbon nanotube with a vacancy. This scheme is based on a Green's Function formalism to treat a non-equilibrium problem, coupled to the Density Functional Theory to describe the electronic structure. We describe a procedure to calculate charge transport properties across a nanosystem. Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970, São Paulo, SP, Brazil Density functional theory method for non-equilibrium charge transport calculations: TRANSAMPAįrederico D.
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