  We present a comprehensive first-principles study of the ballistic transport
properties of low dimensional nanostructures such as linear chains of atoms
(Al, C) and carbon nanotubes in presence of defects. A novel approach is
introduced where quantum conductance is computed from the combination of
accurate plane-wave electronic structure calculations, the evaluation of the
corresponding maximally-localized Wannier functions, and the calculation of
transport properties by a real-space Green's function method based on the
Landauer formalism. This approach is computationally very efficient, can be
straightforwardly implemented as a post-processing step in a standard
electronic-structure calculation, and allows to directly link the electronic
transport properties of a device to the nature of the chemical bonds, providing
insight onto the mechanisms that govern electron flow at the nanoscale.
