  We present a systematic study of interference and k-point sampling effects in
the supercell approach to phase-coherent electron transport. We use a
representative tight-binding model to show that interference between the
repeated images is a small effect compared to the error introduced by using
only the Gamma-point for a supercell containing (3,3) sites in the transverse
plane. An insufficient k-point sampling can introduce strong but unphysical
features in the transmission function which can be traced to the presence of
van Hove singularities in the lead. We present a first-principles calculation
of the transmission through a Pt contact which shows that the k-point sampling
is also important for realistic systems.
