First-principles scattering-state approach for nonlinear electrical transport in nanostructures

We present an ab initio scattering-state method for calculating the electrical transport properties of nanostructures at a finite bias voltage. A typical system of interest consists of two semi-infinite crystalline metal probes and a nanostructure (e.g., an atomic wire or a molecule) placed between the probes. The two metal probes have different chemical potentials at a finite bias voltage. The electronic structure of the system is described by the Kohn-Sham density functional method, with appropriate boundary conditions imposed on the electronic density and potential inside the metal probes. We expand the electronic wave functions with pseudoatomic orbitals and directly solve the self-consistent Kohn-Sham equation to obtain the transmission probabilities of electrons incident from either of the probes. The current through the molecule or nanostructure is then obtained by integrating the transmission between the two chemical potentials. Our scattering-state method provides stable and efficient algorithms for the complex bands, scattering-state wave functions, and the nonequilibrium steady-state electron density. As illustrations of the method, we present the calculated electrical transport properties of a defective carbon nanotube, a four-carbon atomic chain, and a benzene-dithiol molecular junction.