Density-functional method for nonequilibrium electron transport

We describe an ab initio method for calculating the electronic structure,\nelectronic transport, and forces acting on the atoms, for atomic scale systems\nconnected to semi-infinite electrodes and with an applied voltage bias. Our\nmethod is based on the density functional theory (DFT) as implemented in the\nwell tested Siesta approach (which uses non-local norm-conserving\npseudopotentials to describe the effect of the core electrons, and linear\ncombination of finite-range numerical atomic orbitals to describe the valence\nstates). We fully deal with the atomistic structure of the whole system,\ntreating both the contact and the electrodes on the same footing. The effect of\nthe finite bias (including selfconsistency and the solution of the\nelectrostatic problem) is taken into account using nonequilibrium Green's\nfunctions. We relate the nonequilibrium Green's function expressions to the\nmore transparent scheme involving the scattering states. As an illustration,\nthe method is applied to three systems where we are able to compare our results\nto earlier ab initio DFT calculations or experiments, and we point out\ndifferences between this method and existing schemes. The systems considered\nare: (1) single atom carbon wires connected to aluminum electrodes with\nextended or finite cross section, (2) single atom gold wires, and finally (3)\nlarge carbon nanotube systems with point defects.\n