  Based on density functional theory (DFT), we have developed algorithms and a
program code to investigate the electron transport characteristics for a
variety of nanometer scaled devices in the presence of an external bias
voltage. We employed basis sets comprised of linear combinations of numerical
type atomic orbitals and k-point sampling for the realistic modeling of the
bulk electrode. The scheme coupled with the matrix version of the
non-equilibrium Green function method enables determination of the transmission
coefficients at a given energy and voltage in a self-consistent manner, as well
as the corresponding current-voltage (I-V) characteristics. This scheme has
advantages because it is applicable to large systems, easily transportable to
different types of quantum chemistry packages, and extendable to describe
time-dependent phenomena or inelastic scatterings. It has been applied to
diverse types of practical electronic devices such as carbon nanotubes,
graphene nano-ribbons, metallic nanowires, and molecular electronic devices.
The quantum conductance phenomena for systems involving quantum point contacts
and I-V curves are described for the dithiol-benzene molecule in contact with
two Au electrodes using the k-point sampling method.
