  We present a real-space method for first-principles nano-scale electronic
transport calculations. We use the non-equilibrium Green's function method with
density functional theory and implement absorbing boundary conditions (ABCs,
also known as complex absorbing potentials, or CAPs) to represent the effects
of the semi-infinite leads. In real space, the Kohn-Sham Hamiltonian matrix is
highly sparse. As a result, the transport problem parallelizes naturally and
can scale favorably with system size, enabling the computation of conductance
in relatively large molecular junction models. Our use of ABCs circumvents the
demanding task of explicitly calculating the leads' self-energies from surface
Green's functions, and is expected to be more accurate than the use of the
jellium approximation. In addition, we take advantage of the sparsity in real
space to solve efficiently for the Green's function over the entire energy
range relevant to low-bias transport. We illustrate the advantages of our
method with calculations on several challenging test systems and find good
agreement with reference calculation results.
