  We present an efficient numerical approach for treating ballistic quantum
transport across devices described by tight binding (TB) Hamiltonians
designated to systems with localized potential defects. The method is based on
the wave function matching approach, Lippmann-Schwinger equation (LEQ) and the
scattering matrix formalism. We show that the number of matrix elements of the
Green's function to be evaluated for the unperturbed system can be essentially
reduced by projection of the time reversed scattering wave functions on LEQ
which radically improves the speed and lowers the memory consumption of the
calculations. Our approach can be applied to quantum devices of an arbitrary
geometry and any number of degrees of freedom or leads attached. We provide a
couple of examples of possible applications of the theory, including current
equilibration at the p-n junction in graphene and scanning gate microscopy
mapping of electron trajectories in the magnetic focusing experiment on a
graphene ribbon. Additionally, we provide a simple toy example of electron
transport through 1D wire with added onsite perturbation and obtain a simple
formula for conductance showing that Green's function of the device can be
obtained from the conductance versus impurity strength characteristics.
